A279831 - OEIS

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A279831

Numbers that are centered k-gonal numbers for two or more values of k.

1, 7, 13, 16, 19, 22, 25, 31, 37, 43, 46, 49, 55, 61, 64, 67, 73, 76, 79, 85, 91, 97, 103, 106, 109, 111, 115, 121, 127, 133, 136, 139, 141, 145, 148, 151, 154, 157, 163, 166, 169, 172, 175, 181, 187, 190, 191, 193, 196, 199, 205, 211, 217, 221, 223, 226, 229, 232, 235, 241, 247, 253, 256

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

OFFSET

1,2

COMMENTS

Numbers satisfying 1 + n*m*(m+1)/2 for two or more values of (n,m), where n>=0 m>1.

Numbers in this sequence appear in A101321 at least three times (because the second column contains every positive integer).

LINKS

Daniel Sterman, Table of n, a(n) for a(n)<1000

EXAMPLE

19 is in the sequence because 19 is both a centered triangular number and a centered hexagonal number.

CROSSREFS

Cf. A090428 (rough equivalent for polygonal numbers).