G.f.: 1/(1-x)^4 * Product_{k>=1} (1 + x^k).

Terms

a(0) =1a(1) =5a(2) =15a(3) =36a(4) =75a(5) =142a(6) =251a(7) =421a(8) =677a(9) =1052a(10) =1589a(11) =2343a(12) =3384a(13) =4800a(14) =6701a(15) =9224a(16) =12538a(17) =16850a(18) =22413a(19) =29534a(20) =38584a(21) =50010a(22) =64348a(23) =82238a(24) =104442a(25) =131864a(26) =165573a(27) =206830a(28) =257118a(29) =318176