Centered tetrahedral numbers.

Terms

a(0) =1a(1) =5a(2) =15a(3) =35a(4) =69a(5) =121a(6) =195a(7) =295a(8) =425a(9) =589a(10) =791a(11) =1035a(12) =1325a(13) =1665a(14) =2059a(15) =2511a(16) =3025a(17) =3605a(18) =4255a(19) =4979a(20) =5781a(21) =6665a(22) =7635a(23) =8695a(24) =9849a(25) =11101a(26) =12455a(27) =13915a(28) =15485a(29) =17169