A027669 - OEIS

A027669

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

3, 4, 6, 8, 10, 11, 14, 17, 20, 23, 26, 29, 30, 32, 35, 38, 41, 43, 44, 47, 50, 53, 56, 59, 60, 62, 65, 68, 71, 74, 77, 80, 83, 86, 88, 89, 92, 95, 98, 101, 104, 107, 110, 113, 116, 119, 122, 125, 128, 131, 134, 137, 140, 143, 145, 146, 149, 152, 155, 158, 161, 164, 167, 170, 173, 176, 179, 182, 185, 188, 191, 194, 197, 200, 203, 206, 209, 212, 215, 218, 221, 224, 227, 230, 233, 236, 239, 242, 245, 248, 251, 254, 257, 260, 263, 266, 269, 272, 275, 276

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

The m-th k-gonal number is m+(k-2)*(m^2-m)/2.

3*j+2 = A016789(j) is a term for j >= 2.

LINKS

Table of n, a(n) for n=1..100.

FORMULA

Set union of A027696 and A016789, excluding elements 2 and 5. - Max Alekseyev, Feb 27 2025

CROSSREFS

Cf. A016789, A027696, A344410.