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A226890 E.g.f.: exp( Sum_{n>=1} sigma(n,n) * x^(n^2) / n^n ). 1
1, 1, 1, 1, 31, 151, 451, 1051, 33601, 663601, 5187001, 25905001, 254322751, 10408719751, 128046088171, 920598820051, 29249420054401, 723848667813601, 12441294278905201, 138598703861148241, 4406639731521827551, 93453608310743628151, 1932981245635597160851, 27744052310106087405451 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

Here sigma(n,n) = A023887(n), the sum of the n-th powers of the divisors of n.

Compare to: exp( Sum_{n>=1} sigma(n)*x^n/n ), the g.f. of the partitions.

LINKS

Table of n, a(n) for n=0..23.

FORMULA

a(n) == 1 (mod 30) (conjecture - valid up to n=4000; if true for n>=0, why?).

EXAMPLE

E.g.f.: A(x) = 1 + x + x^2/2! + x^3/3! + 31*x^4/4! + 151*x^5/5! + 451*x^6/6! +...

where

log(A(x)) = x + 5*x^4/2^2 + 28*x^9/3^3 + 273*x^16/4^4 + 3126*x^25/5^5 + 47450*x^36/6^6 + 823544*x^49/7^7 +...+ A023887(n)*x^(n^2)/n^n +...

PROG

(PARI) {a(n)=n!*polcoeff(exp(sum(m=1, n, sigma(m, m)*(x^m/m)^m)+x*O(x^n)), n)}

for(n=0, 30, print1(a(n), ", "))

CROSSREFS

Cf. A226838, A023887.

Sequence in context: A126418 A142792 A201964 * A104049 A176922 A134553

Adjacent sequences:  A226887 A226888 A226889 * A226891 A226892 A226893

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jun 20 2013

STATUS

approved

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Last modified November 15 19:54 EST 2018. Contains 317240 sequences. (Running on oeis4.)