Second pentagonal numbers with odd index: a(n) = (2*n-1)*(3*n-1).

Terms

a(0) =1a(1) =2a(2) =15a(3) =40a(4) =77a(5) =126a(6) =187a(7) =260a(8) =345a(9) =442a(10) =551a(11) =672a(12) =805a(13) =950a(14) =1107a(15) =1276a(16) =1457a(17) =1650a(18) =1855a(19) =2072a(20) =2301a(21) =2542a(22) =2795a(23) =3060a(24) =3337a(25) =3626a(26) =3927a(27) =4240a(28) =4565a(29) =4902