G.f.: sqrt(1 + 2*Sum_{n>=1} 2^n*x^(n^2)).

Terms

a(0) =1a(1) =2a(2) =-2a(3) =4a(4) =-6a(5) =20a(6) =-60a(7) =184a(8) =-586a(9) =1908a(10) =-6284a(11) =21032a(12) =-71260a(13) =243928a(14) =-842456a(15) =2931984a(16) =-10272586a(17) =36203996a(18) =-128262540a(19) =456526584a(20) =-1631731284a(21) =5854243512a(22) =-21075615496a(23) =76110581584a(24) =-275644817124