G.f.: Product_{k>=1} (1 + 3*x^(k^2)) / (1-x^k).

Terms

a(0) =1a(1) =4a(2) =5a(3) =9a(4) =17a(5) =34a(6) =47a(7) =75a(8) =109a(9) =165a(10) =240a(11) =341a(12) =473a(13) =671a(14) =936a(15) =1268a(16) =1722a(17) =2325a(18) =3091a(19) =4099a(20) =5403a(21) =7083a(22) =9207a(23) =11923a(24) =15339a(25) =19682a(26) =25134a(27) =31909a(28) =40378a(29) =50954