A080203 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A080203

Steffi sequence; the numbers of pairs of unequal permutations of all the digits 1, ..., b-1 in base b whose ratio is an integer.

0, 0, 1, 1, 25, 7, 623, 1183, 24603, 5895, 2017603, 242283

(list; graph; refs; listen; history; text; internal format)

OFFSET

2,5

COMMENTS

Terms computed by Michael Trott.

LINKS

Table of n, a(n) for n=2..13.

Eric Weisstein's World of Mathematics, Steffi Problem

EXAMPLE

In base 2, there are no solutions for 1, so a(2)=0. In base 3, there are no solutions for 12, so a(3)=0. In base 4, there is a single solutions for 123, so a(4)=1. In base 5, there is a single solution with the digits 1234: 4312_5/1234_5 = 3, so a(5)=1.

MATHEMATICA

f[n_] := Block[{p = FromDigits[ #, n] & /@ Permutations[ Range[n - 1]]}, Sum[ Length[ Select[ p/p[[i]], IntegerQ[ # ] &]], {i, (n - 1)!}] - (n - 1)! ]; Table[ f[n], {n, 2, 9}] (* Robert G. Wilson v, Jul 15 2005 *)

CROSSREFS

T(b-1, b) entries of A080202.

Sequence in context: A243092 A126837 A248583 * A040605 A307179 A065910

Adjacent sequences: A080200 A080201 A080202 * A080204 A080205 A080206

KEYWORD

nonn,hard,base,more

AUTHOR

Eric W. Weisstein, Feb 05 2003

EXTENSIONS

Prepended a(2)=0, added a(13) - Giovanni Resta, Feb 24 2013

STATUS

approved