G.f.: A(x) = Sum_{k>=0} x^k * (1+x)^(k*(k+1)/2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =27a(6) =81a(7) =262a(8) =910a(9) =3363a(10) =13150a(11) =54135a(12) =233671a(13) =1053911a(14) =4951997a(15) =24177536a(16) =122381035a(17) =640937746a(18) =3466900453a(19) =19337255086a(20) =111057640382a(21) =655892813805