Truncated triangular pyramid numbers: a(n) = Sum_{k=4..n} (k*(k+1)/2 - 9).

Terms

a(0) =1a(1) =7a(2) =19a(3) =38a(4) =65a(5) =101a(6) =147a(7) =204a(8) =273a(9) =355a(10) =451a(11) =562a(12) =689a(13) =833a(14) =995a(15) =1176a(16) =1377a(17) =1599a(18) =1843a(19) =2110a(20) =2401a(21) =2717a(22) =3059a(23) =3428a(24) =3825a(25) =4251a(26) =4707a(27) =5194a(28) =5713a(29) =6265