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 A163921 G.f.: A(x) = exp( Sum_{n>=1} A( sigma(n)*x )^n*x^n/n ). 0
 1, 1, 2, 7, 41, 385, 5769, 139541, 5551356, 369312953, 41588540350, 7987225089655, 2629160183190431, 1487755631073862696, 1450453417949809255147, 2439516473122553169216351, 7086426394313598512496200542 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Conjecture: if F(x) = exp( Sum_{n>=1} L(n)*x^n/n ) is an integer series, then the g.f. that satisfies: G(x) = exp( Sum_{n>=1} G( L(n)*x )^n*x^n/n ) is also an integer series. Another example of this is A157675 in which L(n) = 2^n. LINKS Table of n, a(n) for n=0..16. EXAMPLE G.f.: A(x) = 1 + x + 2*x^2 + 7*x^3 + 41*x^4 + 385*x^5 + 5769*x^6 +... log(A(x)) = A(x)*x + A(3x)^2*x^2/2 + A(4x)^3*x^3/3 + A(7x)^4*x^4/4 +... PROG (PARI) {a(n)=local(A=1+x); for(i=1, n, A=exp(sum(k=1, n, subst(A, x, sigma(k)*x+x*O(x^n))^k*x^k/k))); polcoeff(A, n)} CROSSREFS Cf. A157675 (variant), A000203 (sigma). Sequence in context: A006846 A047864 A173916 * A213434 A331920 A008934 Adjacent sequences: A163918 A163919 A163920 * A163922 A163923 A163924 KEYWORD nonn AUTHOR Paul D. Hanna, Sep 01 2009 STATUS approved

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Last modified June 4 21:13 EDT 2023. Contains 363130 sequences. (Running on oeis4.)