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A279831 Numbers that are centered k-gonal numbers for two or more values of k. 1
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).

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

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

Sequence in context: A233301 A274255 A233747 * A102797 A233062 A205686

Adjacent sequences: A279828 A279829 A279830 * A279832 A279833 A279834

KEYWORD

nonn

AUTHOR

Daniel Sterman, Dec 20 2016

STATUS

approved

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Last modified February 2 03:35 EST 2023. Contains 359997 sequences. (Running on oeis4.)