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Search: id:A080203
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| A080203 |
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Steffi sequence; the numbers of pairs of unequal permutations of all the digits 1, ..., b-1 in base b whose ratio is an integer. |
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+0
2
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OFFSET
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2,4
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COMMENT
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Terms computed by Michael Trott.
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LINKS
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Eric Weisstein's World of Mathematics, Steffi Problem
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EXAMPLE
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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.
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MATHEMATICA
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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}] (from Robert G. Wilson v (rgwv(at)rgwv.com), Jul 15 2005)
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CROSSREFS
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T(b-1, b) entries of A080202.
Sequence in context: A040606 A091736 A126837 this_sequence A040605 A065910 A096521
Adjacent sequences: A080200 A080201 A080202 this_sequence A080204 A080205 A080206
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KEYWORD
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nonn,hard,more
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AUTHOR
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Eric Weisstein (eric(AT)weisstein.com), Feb 05, 2003
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