a(n) = (3*n - 1)*(4*n - 1).

Terms

a(0) =1a(1) =6a(2) =35a(3) =88a(4) =165a(5) =266a(6) =391a(7) =540a(8) =713a(9) =910a(10) =1131a(11) =1376a(12) =1645a(13) =1938a(14) =2255a(15) =2596a(16) =2961a(17) =3350a(18) =3763a(19) =4200a(20) =4661a(21) =5146a(22) =5655a(23) =6188a(24) =6745a(25) =7326a(26) =7931a(27) =8560a(28) =9213a(29) =9890