27-gonal pyramidal numbers: a(n) = n*(n+1)*(25*n-22)/6.

Terms

a(0) =0a(1) =1a(2) =28a(3) =106a(4) =260a(5) =515a(6) =896a(7) =1428a(8) =2136a(9) =3045a(10) =4180a(11) =5566a(12) =7228a(13) =9191a(14) =11480a(15) =14120a(16) =17136a(17) =20553a(18) =24396a(19) =28690a(20) =33460a(21) =38731a(22) =44528a(23) =50876a(24) =57800a(25) =65325a(26) =73476a(27) =82278a(28) =91756a(29) =101935