E.g.f.: Product_{n>=1} (exp(2*x^n) + 1)/2.

Terms

a(0) =1a(1) =1a(2) =4a(3) =16a(4) =104a(5) =696a(6) =6272a(7) =57856a(8) =652416a(9) =7657600a(10) =104244992a(11) =1475430144a(12) =23426373632a(13) =387521615872