A073112 Number of permutations p from (1,2,3,...,n) to (1,2,3,...,n) such that 1/(1+p(1)) + 1/(2+p(2)) + ... + 1/(n+p(n)) is an integer.

0, 0, 0, 1, 0, 7, 6, 30, 110, 278, 1332, 3312

Offset

1,6

Links

Table of n, a(n) for n=1..12.

Zhi-Wei Sun, On permutations of {1, ..., n} and related topics, arXiv:1811.10503 [math.CO], 2018.

Prog

(PARI) a(n)=sum(k=1, n!, if(frac(sum(i=1, n, 1/(i+component(numtoperm(n, k), i)))), 0, 1))

Crossrefs

Sequence in context: A341289 A322049 A163260 * A070425 A163842 A328697

Adjacent sequences: A073109 A073110 A073111 * A073113 A073114 A073115

Keyword

nonn,more

Author

Benoit Cloitre, Aug 19 2002

Extensions

More terms from Ryan Propper, Jun 11 2006

Status

approved