21-gonal numbers: a(n) = n*(19n - 17)/2.

Terms

a(0) =0a(1) =1a(2) =21a(3) =60a(4) =118a(5) =195a(6) =291a(7) =406a(8) =540a(9) =693a(10) =865a(11) =1056a(12) =1266a(13) =1495a(14) =1743a(15) =2010a(16) =2296a(17) =2601a(18) =2925a(19) =3268a(20) =3630a(21) =4011a(22) =4411a(23) =4830a(24) =5268a(25) =5725a(26) =6201a(27) =6696a(28) =7210a(29) =7743