Centered 20-gonal (or icosagonal) numbers.

Terms

a(0) =1a(1) =21a(2) =61a(3) =121a(4) =201a(5) =301a(6) =421a(7) =561a(8) =721a(9) =901a(10) =1101a(11) =1321a(12) =1561a(13) =1821a(14) =2101a(15) =2401a(16) =2721a(17) =3061a(18) =3421a(19) =3801a(20) =4201a(21) =4621a(22) =5061a(23) =5521a(24) =6001a(25) =6501a(26) =7021a(27) =7561a(28) =8121a(29) =8701