A279831 - OEIS

%I #12 Mar 13 2017 04:25:56

%S 1,7,13,16,19,22,25,31,37,43,46,49,55,61,64,67,73,76,79,85,91,97,103,

%T 106,109,111,115,121,127,133,136,139,141,145,148,151,154,157,163,166,

%U 169,172,175,181,187,190,191,193,196,199,205,211,217,221,223,226,229,232,235,241,247,253,256

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

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

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

%H Daniel Sterman, <a href="/A279831/b279831.txt">Table of n, a(n) for a(n)<1000</a>

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

%Y Cf. A090428 (rough equivalent for polygonal numbers).

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

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

%K nonn

%O 1,2

%A _Daniel Sterman_, Dec 20 2016