A016021 Number of permutations of {1,2,...,n} in which each element follows its proper divisors.

1, 1, 1, 2, 3, 12, 25, 150, 378, 1960, 8154, 81540, 261250, 3135000, 19358040, 160331626, 719579700, 11513275200, 62702704800, 1128648686400, 7122671957664, 88475482100520, 905279068633800, 19916139509943600

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 A349016

Adjacent sequences: A016018 A016019 A016020 * A016022 A016023 A016024

Keyword

nonn

Author

David W. Wilson, Jun 07 2000

Status

approved