a(n) = A115004(2n)/4.

Terms

a(0) =2a(1) =20a(2) =83a(3) =237a(4) =534a(5) =1054a(6) =1892a(7) =3114a(8) =4880a(9) =7327a(10) =10530a(11) =14730a(12) =20066a(13) =26689a(14) =34882a(15) =44902a(16) =56850a(17) =70946a(18) =87644a(19) =106986a(20) =129470a(21) =155457a(22) =184920a(23) =218596a(24) =256675a(25) =299292a(26) =347261a(27) =400590a(28) =459615a(29) =525217