a(n) = (9*n + 6)^3.

Terms

a(0) =216a(1) =3375a(2) =13824a(3) =35937a(4) =74088a(5) =132651a(6) =216000a(7) =328509a(8) =474552a(9) =658503a(10) =884736a(11) =1157625a(12) =1481544a(13) =1860867a(14) =2299968a(15) =2803221a(16) =3375000a(17) =4019679a(18) =4741632a(19) =5545233a(20) =6434856a(21) =7414875a(22) =8489664