

A080203


Steffi sequence; the numbers of pairs of unequal permutations of all the digits 1, ..., b1 in base b whose ratio is an integer.


1



0, 0, 1, 1, 25, 7, 623, 1183, 24603, 5895, 2017603, 242283
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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(b1, 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



