12 times triangular numbers.

Terms

a(0) =0a(1) =12a(2) =36a(3) =72a(4) =120a(5) =180a(6) =252a(7) =336a(8) =432a(9) =540a(10) =660a(11) =792a(12) =936a(13) =1092a(14) =1260a(15) =1440a(16) =1632a(17) =1836a(18) =2052a(19) =2280a(20) =2520a(21) =2772a(22) =3036a(23) =3312a(24) =3600a(25) =3900a(26) =4212a(27) =4536a(28) =4872a(29) =5220