login
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
OFFSET
0,4
LINKS
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
KEYWORD
nonn
AUTHOR
David W. Wilson, Jun 07 2000
STATUS
approved