Second pentagonal numbers: a(n) = n*(3*n + 1)/2.

Terms

a(0) =0a(1) =2a(2) =7a(3) =15a(4) =26a(5) =40a(6) =57a(7) =77a(8) =100a(9) =126a(10) =155a(11) =187a(12) =222a(13) =260a(14) =301a(15) =345a(16) =392a(17) =442a(18) =495a(19) =551a(20) =610a(21) =672a(22) =737a(23) =805a(24) =876a(25) =950a(26) =1027a(27) =1107a(28) =1190a(29) =1276