[seqfan] Closed form?

[David Wilson]

Is there a closed form for

f(x) = SUM(k = 0 to inf; x^k/(2^((k^2-k)/2)*k!)))

i.e;

f(x) = 1 + x + x^2/4 + x^3/48 + x^4/1536 + x^5/122880 + ...