1,2

Or, a(n) = Sum_{ d divides n } n!/d. - Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jul 24 2005

Number of labeled regular octopi (or octopuses, cycles of ordered sets all the same size).

F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Camb. 1998, p. 56 (1.4.67).

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 159, #10, A(n,1).

T. D. Noe, Table of n, a(n) for n=1..100

H. Ochiai, Counting functions for branched covers of elliptic curves and quasi-modular forms

a(p) = (p+1)*(p-1)! if p is a prime. - Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jul 24 2005

E.g.f.: log(f(x)), where f(x) = o.g.f. for partitions (A000041), Product_{k=1..inf} 1/(1-x^k) - njas.

E.g.f.: Sum_{k>0} x^k/(k*(1-x^k)). - Vladeta Jovovic (vladeta(AT)Eunet.yu), Mar 27 2005

a(6) = 6!{1/1 +1/2 +1/3 + 1/6}=1440.

with(numtheory): a:=proc(n) local div: div:=divisors(n): n!*sum(1/div[j], j=1..tau(n)) end: seq(a(n), n=1..23); (Deutsch)

Left edge of triangle in A008298. Cf. A058892.

Cf. A057625.

Cf. A110373, A110374.

Sequence in context: A107991 A007175 A128322 this_sequence A051763 A074435 A039647

Adjacent sequences: A038045 A038046 A038047 this_sequence A038049 A038050 A038051

easy,nonn,nice

Christian G. Bower (bowerc(AT)usa.net)

More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Jul 24 2005

Edited by njas, May 12 2008 at the suggestion of Joerg Arndt.