Rhombic matchstick numbers: a(n) = n*(3*n+2).

Terms

a(0) =0a(1) =5a(2) =16a(3) =33a(4) =56a(5) =85a(6) =120a(7) =161a(8) =208a(9) =261a(10) =320a(11) =385a(12) =456a(13) =533a(14) =616a(15) =705a(16) =800a(17) =901a(18) =1008a(19) =1121a(20) =1240a(21) =1365a(22) =1496a(23) =1633a(24) =1776a(25) =1925a(26) =2080a(27) =2241a(28) =2408a(29) =2581