Hexagonal matchstick numbers: a(n) = 3*n*(3*n+1).

Terms

a(0) =0a(1) =12a(2) =42a(3) =90a(4) =156a(5) =240a(6) =342a(7) =462a(8) =600a(9) =756a(10) =930a(11) =1122a(12) =1332a(13) =1560a(14) =1806a(15) =2070a(16) =2352a(17) =2652a(18) =2970a(19) =3306a(20) =3660a(21) =4032a(22) =4422a(23) =4830a(24) =5256a(25) =5700a(26) =6162a(27) =6642a(28) =7140a(29) =7656