G.f.: 1/(1-x)^3 * Product_{k>=1} (1 + x^k).

Terms

a(0) =1a(1) =4a(2) =10a(3) =21a(4) =39a(5) =67a(6) =109a(7) =170a(8) =256a(9) =375a(10) =537a(11) =754a(12) =1041a(13) =1416a(14) =1901a(15) =2523a(16) =3314a(17) =4312a(18) =5563a(19) =7121a(20) =9050a(21) =11426a(22) =14338a(23) =17890a(24) =22204a(25) =27422a(26) =33709a(27) =41257a(28) =50288a(29) =61058