A090428 Numbers that are k-gons for two or more k's, where k = 3, 4, 5, ..., 16.

1, 6, 9, 10, 12, 15, 16, 21, 28, 36, 45, 55, 64, 66, 70, 81, 91, 105, 120, 145, 153, 171, 176, 190, 196, 210, 225, 231, 276, 280, 325, 378, 400, 435, 441, 477, 496, 540, 561, 595, 616, 630, 651, 703, 715, 780, 833, 861, 936, 946, 1035, 1089, 1105, 1128, 1216

Offset: 1

Author

Eric W. Weisstein, Nov 30 2003

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Polygonal Number.

Crossrefs

Cf. A062712, A090466.

Programs

PARI

is(n,c=2)=for(s=3,16, ispolygonal(n,s)&&!c--&&return(s)) \\ M. F. Hasler, Jan 19 2017