G.f.: exp( Sum_{n>=1} [Sum_{k=0..2*n} C(2*n,k)^2 *x^k] *x^n/n ).

Terms

a(0) =1a(1) =1a(2) =5a(3) =14a(4) =52a(5) =187a(6) =708a(7) =2734a(8) =10758a(9) =43004a(10) =174004a(11) =711660a(12) =2936564a(13) =12211688a(14) =51124185a(15) =215299685a(16) =911445413a(17) =3876523626a(18) =16556573129a(19) =70980163570a(20) =305343924258