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A016021 Number of permutations of {1,2,...,n} in which each element follows its proper divisors. 1
1, 1, 1, 2, 3, 12, 25, 150, 378, 1960, 8154, 81540, 261250, 3135000, 19358040, 160331626, 719579700, 11513275200, 62702704800, 1128648686400, 7122671957664, 88475482100520, 905279068633800, 19916139509943600 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Sean A. Irvine, Table of n, a(n) for n = 0..45

EXAMPLE

12 valid permutations for a(5): 12345 12354 12435 12453 12534 12543 13245 13254 13524 15234 15243 15324.

CROSSREFS

Sequence in context: A148069 A148070 A187994 * A173669 A136703 A249490

Adjacent sequences:  A016018 A016019 A016020 * A016022 A016023 A016024

KEYWORD

nonn

AUTHOR

David W. Wilson, Jun 07 2000

STATUS

approved

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Last modified July 23 17:34 EDT 2021. Contains 346259 sequences. (Running on oeis4.)