Doubly triangular numbers: a(n) = n*(n+1)*(n^2+n+2)/8.

Terms

a(0) =0a(1) =1a(2) =6a(3) =21a(4) =55a(5) =120a(6) =231a(7) =406a(8) =666a(9) =1035a(10) =1540a(11) =2211a(12) =3081a(13) =4186a(14) =5565a(15) =7260a(16) =9316a(17) =11781a(18) =14706a(19) =18145a(20) =22155a(21) =26796a(22) =32131a(23) =38226a(24) =45150a(25) =52975a(26) =61776a(27) =71631a(28) =82621a(29) =94830