15 times triangular numbers.

Terms

a(0) =0a(1) =15a(2) =45a(3) =90a(4) =150a(5) =225a(6) =315a(7) =420a(8) =540a(9) =675a(10) =825a(11) =990a(12) =1170a(13) =1365a(14) =1575a(15) =1800a(16) =2040a(17) =2295a(18) =2565a(19) =2850a(20) =3150a(21) =3465a(22) =3795a(23) =4140a(24) =4500a(25) =4875a(26) =5265a(27) =5670a(28) =6090a(29) =6525