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

Offset: 1

Author

Daniel Sterman, Dec 20 2016

Keywords

• nonn

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).

Examples

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

Links

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

Crossrefs

Cf. A090428 (rough equivalent for polygonal numbers).

Cf. A101321 (table of all centered polygonal numbers).

Cf. A275340 (list of nontrivial centered polygonal numbers).