Ian Stewart berichtet in (1) – einem Beitrag gegen den Unsinn z.B. in Intelligenztests Zahlenfolgen mit "passenden" Folgengliedern fortzusetzen – von einer e-mail-Adresse, über die Informationen über ganzzahlige Folgen abgerufen werden können.

(Zum Thema Zahlenunsinn siehe auch (2).)

Man schickt dabei die ersten Glieder einer Folge an einen Computer der AT&T Bell und bekommt Auskunft, ob eine von mehr als 5000 bekannnten Folgen so anfängt.

An die E-mail-Adresse sequences@research.att.com

wird folgender Text geschickt:

To: sequences@research.att.com

lookup 3 1 4 1 5 9

Als Antwort erhält man folgende e-mail:

From: sequences-reply@research.att.com

Matches (at most 7) found for 3 1 4 1 5 9 :

%I A0796 M2218 N0880

%S A0796

3,1,4,1,5,9,2,6,5,3,5,8,9,7,9,3,2,3,8,4,6,2,6,4,3,3,8,3,2,7,9,5,

%T A0796

0,2,8,8,4,1,9,7,1,6,9,3,9,9,3,7,5,1,0,5,8,2,0,9,7,4,9,4,4,5,9,2,3,0,7,8,

%U A0796 1,6,5

%N A0796 Decimal expansion of $pi$.

%R A0796 MOC 16 80 62.

%O A0796 1,1

%B A0796 A0796.

%C A0796 njas

%Z A0796 FLAG.

%K A0796 cons,nonn

References (if any):

[MOC] = { Mathematics of Computation} (formerly { Mathematical Tables and

Other Aids to Computation}).

o See also my Integer Sequences web page:

ftp://netlib.att.com/netlib/att/math/sloane/doc/eistop.html

o For more sequences see "The Encyclopedia of Integer Sequences"

by N. J. A. Sloane & S. Plouffe, Academic Press, ISBN 0-12-558630-2.

o If the sequence you looked up was not in the table and you think it

should be, send it to me at njas@research.att.com

o There is a second sequence server (superseeker@research.att.com)

that tries hard to find an explanation. Only 1 request per person

per hour please.

o Key: %I = ID line: Annnn = absolute catalogue number of sequence,

Mnnn = number in the Encyclopedia,

%S, %T, %U = beginning of sequence, [%V,%W,%X = signed version]

%N = name, %R = references, %Y = cross-references, %A = authority,

%F = formula, %K = keywords,

%a = Macsyma; %c = C; %f = Fortran; %g = Gap; %i = Pari;

%m = Magma; %p = Maple; %t = Mathematica; %s = S

%O = offset = [a,b]: a is subscript of first entry, b gives the

position of the first entry >= 2.

References to journals give volume, page, year.

o If the word "lookup" does not appear you will be sent the help file.

Sequentially yours, The On-Line Encyclopedia of Integer Sequences,

N. J. A. Sloane, Bell Labs, Murray Hill NJ 07974 USA njas@research.att.com

Zusätzlich habe ich folgende e-mail mit Erklärungen erhalten:

From: njas@research.att.com

Greetings from

The On-Line Encyclopedia of Integer Sequences

N. J. A. Sloane

AT&T Bell Labs, Murray Hill, New Jersey

with the assistance of Simon Plouffe

Centre for Experimental & Constructive Mathematics, Burnaby BC, Canada

INSTRUCTIONS: ...

RECOMMENDATIONS:

. If you receive 7 matches, try again giving more terms

. Minus signs should be omitted, since the table only records

the absolute values of the terms

. For a sequence of rational numbers, try the numerators

and denominators separately

. For an array of numbers, try looking up the individual

rows, columns or diagonals, whichever seem appropriate

. Only infinite sequences are included (although there are

a few exceptions)

. It may be advisable to omit the intial terms, since

there may be several ways to begin the sequence

. Give as many terms as possible (although if you give

more terms than are in the table, the program will

not find a match - so don't give TOO many!)

NOTATION USED IN THE ENCYCLOPEDIA

%I = identification line:

Annnn = absolute catalogue number of sequence,

Mnnnn = number in "The Encyclopedia of Integer Sequences"

by N.J.A. Sloane and S. Plouffe, Academic Press, San Diego, CA, 1995.

Nnnnn = number (if any) in "Handbook of Integer Sequences" (1973)

%S, %T, %U = beginning of sequence (with all signs omitted)

%V, %W, %X = signed version of sequence if appropriate and if known

(we are gradually adding these)

%N = name

%R = references

references to journals give volume, page, year.

%Y = cross-references to other sequences

%F = formula (if not included in %N line),

%A = authority

%E = errors, updates

%C = checked by

%O = offset = [a,b]: a is subscript of first entry, b gives the

position of the first entry >= 2.

%K = keywords, as follows:

base: dependent on base used for sequence

bref: sequence is too short to do any analysis with

cofr: a continued fraction expansion of a number

cons: a decimal expansion of a number

core: an important sequence

dumb: an unimportant sequence

easy: it is very easy to produce terms of sequence

fini: a finite sequence

frac: numerators or denominators of sequence of rationals

hard: next term not known, may be hard to find.

would someone please extend this sequence?

huge: contains terms too big for Fortran or C

look: need to find out if this sequence contains negative numbers

and if it does we need a copy of the signed version

(see below)

more: we need more terms! would someone please extend this sequence?

nonn: a sequence of nonnegative numbers

sign: sequence contains negative numbers

we need %V, %W, %X lines (matching the %S,T,U lines)

giving the signed sequence

tabl: typically a triangle of numbers, such as Pascal's triangle,

made into a sequence by reading it row by row.

word: depends on words in some language for the sequence

We are slowly adding computer programs to compute the sequences.

They have to fit on one line but the line can be long.

Contributions will be welcomed. Languages so far:

%a = Macsyma; %c = C; %f = Fortran; %g = Gap; %i = Pari;

%m = Magma; %p = Maple; %t = Mathematica; %s = S

For example if you lookup 1 1 1 1 1 1 1 2 3 4 5 6 7 8 10 13 17 22

you now get (in addition to the other information) the line

%p A5709 f:= proc(n) option remember; if n <=6 then 1; else f(n-1)+f(n-7); fi;

end;

DOCUMENTATION: ...

CONTRIBUTING NEW SEQUENCES:

New sequences, comments, corrections, extensions, etc.,

accompanied whenever possible by references, should be sent to:

N. J. A. Sloane, ATT Bell Labs, Room 2C-376,

600 Mountain Ave, Murray Hill, NJ 07974, USA.

email: njas@research.att.com, fax: 908 582 3340, voice: 908 582 2005

The sequences should be infinite (although some very long finite

ones are also included). Only nonnegative sequences are included:

negative numbers are replaced by their absolute values.

Announcement: Academic Press will publish "The Encyclopedia

of Integer Sequences" by N.J.A. Sloane and S. Plouffe in late

1994 or early 1995. A floppy disk containing just the sequences

will also be available from them. Further info will be posted here.

COMMON ERRORS:...

Literatur:

(1) Stewart Ian: Mathematische Unterhaltungen - Falsche Fibonaccifolgen. In: Spektrum der Wissenschaft, November 1995.

(2) Paulos John Allen: Zahlenblind - Mathematisches Analphabetentum und seine Konsequenzen, München, 1990.