A107944 G.f. A(x) satisfies: A(x) = x/f(x,A(x)) where f(,) is Ramanujan's theta function; i.e., A(x) = x/Sum_{n=-oo,+oo} x^(n*(n+1)/2)*A(x)^(n*(n-1)/2).

1, -2, 6, -22, 88, -376, 1680, -7752, 36660, -176758, 865676, -4294666, 21537584, -109007408, 556096920, -2856490080, 14761719654, -76693856026, 400359733068, -2098903394904, 11045982153266, -58335010518882, 309052004994306, -1642074778175370, 8748018667952754

Offset

1,2

Comments

A variant of sequence A107902 by Michael Somos.

Links

Table of n, a(n) for n=1..25.

Formula

G.f.: A(x) = series_reversion(G107902(x)) where G107902(x) is g.f. of A107902.

Example

A(x) = x - 2*x^2 + 6*x^3 - 22*x^4 + 88*x^5 - 376*x^6 + 1680*x^7 -+...

Prog

(PARI) {a(n)=local(A); if(n<1, 0, A=x+O(x^2); for(k=2, n, A=x/sum(i=-sqrtint(n-1), sqrtint(n+2), x^((i^2+i)/2)*A^((i^2-i)/2))); polcoeff(A, n))}

Crossrefs

Cf. A107902, A107945.

Sequence in context: A379327 A294593 A214358 * A150265 A150266 A165522

Adjacent sequences: A107941 A107942 A107943 * A107945 A107946 A107947

Keyword

sign

Author

Paul D. Hanna, May 28 2005

Status

approved