a(n) = 3*p(n), where p(n) is the number of partitions of n.

Terms

a(0) =3a(1) =3a(2) =6a(3) =9a(4) =15a(5) =21a(6) =33a(7) =45a(8) =66a(9) =90a(10) =126a(11) =168a(12) =231a(13) =303a(14) =405a(15) =528a(16) =693a(17) =891a(18) =1155a(19) =1470a(20) =1881a(21) =2376a(22) =3006a(23) =3765a(24) =4725a(25) =5874a(26) =7308a(27) =9030a(28) =11154a(29) =13695