G.f.: Sum_{n>=0} x^n * Product_{k=0..n-1} (1 + (2*k+1)*x + x^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =15a(5) =47a(6) =150a(7) =522a(8) =1903a(9) =7319a(10) =29396a(11) =122988a(12) =534141a(13) =2400061a(14) =11136516a(15) =53220492a(16) =261576725a(17) =1319629445a(18) =6825232486a(19) =36137198722a(20) =195664517227