Expansion of square of g.f. for A051573.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =11a(5) =26a(6) =58a(7) =142a(8) =351a(9) =890a(10) =2282a(11) =5948a(12) =15624a(13) =41442a(14) =110703a(15) =297676a(16) =804892a(17) =2187490a(18) =5971392a(19) =16366734a(20) =45021391a(21) =124253828a(22) =343956858a(23) =954760502a(24) =2656946827a(25) =7411140120a(26) =20716895918a(27) =58027609028a(28) =162837485745