Central polygonal numbers: a(n) = n^2 - n + 1.

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =13a(5) =21a(6) =31a(7) =43a(8) =57a(9) =73a(10) =91a(11) =111a(12) =133a(13) =157a(14) =183a(15) =211a(16) =241a(17) =273a(18) =307a(19) =343a(20) =381a(21) =421a(22) =463a(23) =507a(24) =553a(25) =601a(26) =651a(27) =703a(28) =757a(29) =813