G.f.: exp( Sum_{n>=0} [ Sum_{k=0..n} C(n,k)^2*x^k ]^2* x^n/n ).

Terms

a(0) =1a(1) =1a(2) =3a(3) =8a(4) =25a(5) =80a(6) =271a(7) =952a(8) =3443a(9) =12758a(10) =48212a(11) =185283a(12) =722227a(13) =2849955a(14) =11366379a(15) =45757142a(16) =185726603a(17) =759401542a(18) =3125472832a(19) =12939604503a(20) =53856950922a(21) =225250407802a(22) =946253665230