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 A205797 G.f.: A(x) = exp( Sum_{n>=1} sigma(n)^4 * x^n/n ). 1
 1, 1, 41, 126, 1526, 5185, 46920, 176865, 1254608, 4986548, 30563031, 123868761, 683127011, 2793828323, 14223836013, 58127497582, 278433541834, 1130954381904, 5159127957638, 20767403083249, 91032595281699, 362455763000997, 1536849042738162 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Compare with g.f. for partition numbers: exp( Sum_{n>=1} sigma(n)*x^n/n ), where sigma(n) = A000203(n) is the sum of the divisors of n. LINKS FORMULA a(n) = (1/n)*Sum_{k=1..n} sigma(k)^4*a(n-k) for n>0, with a(0) = 1. G.f.: exp( Sum_{n>=1} Sum_{k>=1} sigma(n*k)^3 * x^(n*k) / n ). EXAMPLE G.f.: A(x) = 1 + x + 41*x^2 + 126*x^3 + 1526*x^4 + 5185*x^5 +... such that, by definition, log(A(x)) = x + 3^4*x^2/2 + 4^4*x^3/3 + 7^4*x^4/4 + 6^4*x^5/5 + 12^4*x^6/6 +... PROG (PARI) {a(n)=polcoeff(exp(sum(k=1, n, sigma(k)^4*x^k/k)+x*O(x^n)), n)} /* Paul D. Hanna */ (PARI) {a(n)=polcoeff(exp(sum(m=1, n+1, sum(k=1, n\m, sigma(m*k)^3*x^(m*k)/m)+x*O(x^n))), n)} /* Paul D. Hanna */ (PARI) a(n)=if(n==0, 1, (1/n)*sum(k=1, n, sigma(k)^4*a(n-k))) CROSSREFS Cf. A156302, A178933, A000203 (sigma), A000041 (partitions). Sequence in context: A232100 A195038 A067896 * A203804 A142290 A013643 Adjacent sequences:  A205794 A205795 A205796 * A205798 A205799 A205800 KEYWORD nonn AUTHOR Paul D. Hanna, Jan 31 2012 STATUS approved

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Last modified January 17 14:57 EST 2020. Contains 330958 sequences. (Running on oeis4.)