Numbers k such that for some m, the sum of the first m k-gonal numbers is again a k-gonal number.

Terms

a(0) =3a(1) =4a(2) =6a(3) =8a(4) =10a(5) =11a(6) =14a(7) =17a(8) =20a(9) =23a(10) =26a(11) =29a(12) =30a(13) =32a(14) =35a(15) =38a(16) =41a(17) =43a(18) =44a(19) =47a(20) =50a(21) =53a(22) =56a(23) =59a(24) =60a(25) =62a(26) =65a(27) =68a(28) =71a(29) =74