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A209357 G.f. satisfies: A(x) = Product_{n>=1} (1 + x^(n+1)*A(x)) / (1 - x^n). 1
1, 1, 3, 6, 14, 31, 72, 166, 390, 922, 2197, 5273, 12728, 30892, 75327, 184476, 453505, 1118798, 2768843, 6872437, 17103411, 42670102, 106697009, 267359854, 671260241, 1688411587, 4254084396, 10735614274, 27132998096, 68671994940, 174035109012, 441607820562 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..31.

FORMULA

G.f. satisfies: A(x) = Sum_{n>=0} x^n*Product_{k=1..n} (1 + x^k*A(x))/(1-x^k) due to the q-binomial theorem.

EXAMPLE

G.f.: A(x) = 1 + x + 3*x^2 + 6*x^3 + 14*x^4 + 31*x^5 + 72*x^6 + 166*x^7 +...

where the g.f. satisfies the identity:

A(x) = (1+x^2*A(x))/(1-x) * (1+x^3*A(x))/(1-x^2) * (1+x^4*A(x))/(1-x^3) *...

A(x) = 1 + x*(1+x*A(x))/(1-x) + x^2*(1+x*A(x))*(1+x^2*A(x))/((1-x)*(1-x^2)) + x^3*(1+x*A(x))*(1+x^2*A(x))*(1+x^3*A(x))/((1-x)*(1-x^2)*(1-x^3)) +...

PROG

(PARI) {a(n)=local(A=1+x); for(i=1, n, A=prod(m=1, n, (1+x^(m+1)*A)/(1-x^m+x*O(x^n)))); polcoeff(A, n)}

(PARI) {a(n)=local(A=1+x); for(i=1, n, A=sum(m=0, n, x^m*prod(k=1, m, (1+x^k*A)/(1-x^k+x*O(x^n))))); polcoeff(A, n)}

for(n=0, 35, print1(a(n), ", "))

CROSSREFS

Cf. A190861, A190862.

Sequence in context: A199853 A006356 A077998 * A090165 A129954 A238768

Adjacent sequences:  A209354 A209355 A209356 * A209358 A209359 A209360

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Mar 06 2012

STATUS

approved

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Last modified August 8 19:29 EDT 2020. Contains 336298 sequences. (Running on oeis4.)