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 A156234 G.f.: A(x) = exp( Sum_{n>=1} sigma(n)*A000204(n)*x^n/n ). 6
 1, 1, 5, 10, 30, 63, 170, 355, 880, 1875, 4349, 9189, 20810, 43355, 95140, 198247, 424527, 875965, 1849535, 3781820, 7873167, 16005196, 32883560, 66390850, 135198990, 271051271, 546931398, 1090751095, 2183512495, 4329540830 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Compare to g.f. of partition numbers: exp( Sum_{n>=1} sigma(n)*x^n/n ), and to the g.f. of Fibonacci numbers: exp( Sum_{n>=1} A000204(n)*x^n/n ) where A000204 is the Lucas numbers. LINKS Robert Israel, Table of n, a(n) for n = 0..3000 FORMULA a(n) = (1/n)*Sum_{k=1..n} sigma(n)*A000204(k)*a(n-k) for n>0, with a(0) = 1. G.f.: Product_{n>=1} 1/(1 - Lucas(n)*x^n + (-1)^n*x^(2*n)) where Lucas(n) = A000204(n). Logarithmic derivative yields A225528. EXAMPLE G.f.: A(x) = 1 + x + 5*x^2 + 10*x^3 + 30*x^4 + 63*x^5 + 170*x^6 + 355*x^7 + ... log(A(x)) = x + 3*3*x^2/2 + 4*4*x^3/3 + 7*7*x^4/4 + 6*11*x^5/5 + 12*18*x^6/6 + ... Also, the g.f. equals the product: A(x) = 1/((1-x-x^2) * (1-3*x^2+x^4) * (1-4*x^3-x^6) * (1-7*x^4+x^8) * (1-11*x^5-x^10) * (1-18*x^6+x^12) * ... * (1 - Lucas(n)*x^n + (-1)^n*x^(2*n)) * ...). MAPLE N:= 100: # to get a(0) to a(N) G:= exp(add(numtheory:-sigma(n)*lucas(n)*x^n/n, n=1..N)): S:= series(G, x, N+1): seq(coeff(S, x, i), i=0..N); # Robert Israel, Dec 23 2015 PROG (PARI) {a(n)=polcoeff(exp(sum(k=1, n, sigma(k)*(fibonacci(k-1)+fibonacci(k+1))*x^k/k)+x*O(x^n)), n)} for(n=0, 40, print1(a(n), ", ")) (PARI) {Lucas(n)=fibonacci(n-1)+fibonacci(n+1)} {a(n)=polcoeff(prod(m=1, n, 1/(1-Lucas(m)*x^m+(-1)^m*x^(2*m)+x*O(x^n))), n)} for(n=0, 40, print1(a(n), ", ")) CROSSREFS Cf. A225528, A000203 (sigma), A000204 (Lucas), A000041 (partitions), A000045. Sequence in context: A294286 A133629 A156302 * A048010 A002571 A077916 Adjacent sequences:  A156231 A156232 A156233 * A156235 A156236 A156237 KEYWORD nonn AUTHOR Paul D. Hanna, Feb 06 2009 STATUS approved

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Last modified September 28 10:48 EDT 2021. Contains 347714 sequences. (Running on oeis4.)