a(n) = 4*p(n), where p(n) is the number of partitions of n.

Terms

a(0) =4a(1) =4a(2) =8a(3) =12a(4) =20a(5) =28a(6) =44a(7) =60a(8) =88a(9) =120a(10) =168a(11) =224a(12) =308a(13) =404a(14) =540a(15) =704a(16) =924a(17) =1188a(18) =1540a(19) =1960a(20) =2508a(21) =3168a(22) =4008a(23) =5020a(24) =6300a(25) =7832a(26) =9744a(27) =12040a(28) =14872a(29) =18260