Structured truncated tetrahedral numbers.

Terms

a(0) =1a(1) =12a(2) =44a(3) =108a(4) =215a(5) =376a(6) =602a(7) =904a(8) =1293a(9) =1780a(10) =2376a(11) =3092a(12) =3939a(13) =4928a(14) =6070a(15) =7376a(16) =8857a(17) =10524a(18) =12388a(19) =14460a(20) =16751a(21) =19272a(22) =22034a(23) =25048a(24) =28325a(25) =31876a(26) =35712a(27) =39844a(28) =44283a(29) =49040