Pentagonal numbers with odd index: a(n) = (2*n+1)*(3*n+1).

Terms

a(0) =1a(1) =12a(2) =35a(3) =70a(4) =117a(5) =176a(6) =247a(7) =330a(8) =425a(9) =532a(10) =651a(11) =782a(12) =925a(13) =1080a(14) =1247a(15) =1426a(16) =1617a(17) =1820a(18) =2035a(19) =2262a(20) =2501a(21) =2752a(22) =3015a(23) =3290a(24) =3577a(25) =3876a(26) =4187a(27) =4510a(28) =4845a(29) =5192