G.f.: sqrt( Sum_{n>=0} 4^n*x^(n^2) ).

Terms

a(0) =1a(1) =2a(2) =-2a(3) =4a(4) =-2a(5) =12a(6) =-36a(7) =104a(8) =-330a(9) =1068a(10) =-3356a(11) =10808a(12) =-35156a(13) =115192a(14) =-380744a(15) =1267152a(16) =-4242778a(17) =14285644a(18) =-48336684a(19) =164272984a(20) =-560515836a(21) =1919455464a(22) =-6594719992a(23) =22725877680a(24) =-78531331524a(25) =272062125048a(26) =-944738639640