A193235 - OEIS

A193235

G.f.: A(x) = ( Sum_{n>=0} (-4)^n * x^(n^2) )^(-1/2).

1, 2, 6, 20, 62, 204, 684, 2312, 7926, 27436, 95572, 334872, 1178796, 4164984, 14763096, 52471056, 186928422, 667295052, 2386388356, 8547855032, 30661465476, 110125076328, 395989755496, 1425411710064, 5135888179644, 18521445768696, 66847890766152

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

LINKS

Table of n, a(n) for n=0..26.

EXAMPLE

G.f.: A(x) = 1 + 2*x + 6*x^2 + 20*x^3 + 62*x^4 + 204*x^5 + 684*x^6 +...

where

1/A(x)^2 = 1 - 4*x + 16*x^4 - 64*x^9 + 256*x^16 - 1024*x^25 + 4096*x^36 - 16384*x^49 +...+ (-4)^n*x^(n^2) +...

PROG

(PARI) {a(n)=local(S=sum(m=0, sqrtint(n), (-4)^m*x^(m^2))+x*O(x^n)); polcoeff(S^(-1/2), n)}

CROSSREFS

Cf. A193234.

Sequence in context: A052958 A247076 A177792 * A199102 A053730 A220874

Adjacent sequences: A193232 A193233 A193234 * A193236 A193237 A193238

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jul 18 2011

STATUS

approved