G.f. satisfies A(x) = 1/(1-x)^4 + x^4*A(x)^4.

Terms

a(0) =1a(1) =4a(2) =10a(3) =20a(4) =36a(5) =72a(6) =220a(7) =936a(8) =4045a(9) =15836a(10) =56174a(11) =187148a(12) =616651a(13) =2114448a(14) =7717752a(15) =29498000a(16) =114243269a(17) =437915876a(18) =1650264874a(19) =6149423732a(20) =22909545269a(21) =86129798600a(22) =327872238092