20-gonal (or icosagonal) numbers: a(n) = n*(9*n-8).

Terms

a(0) =0a(1) =1a(2) =20a(3) =57a(4) =112a(5) =185a(6) =276a(7) =385a(8) =512a(9) =657a(10) =820a(11) =1001a(12) =1200a(13) =1417a(14) =1652a(15) =1905a(16) =2176a(17) =2465a(18) =2772a(19) =3097a(20) =3440a(21) =3801a(22) =4180a(23) =4577a(24) =4992a(25) =5425a(26) =5876a(27) =6345a(28) =6832a(29) =7337