A133251 Heptagonal numbers A000566 which are the sum of two other heptagonal numbers > 0.

697, 3186, 3744, 5221, 7209, 8323, 12496, 12852, 19228, 20566, 21022, 24850, 29539, 35224, 38254, 40768, 44023, 44689, 52345, 53802, 58293, 62173, 63760, 66178, 67815, 78057, 79834, 80730, 82537, 95746, 97713, 101707, 115240, 131905, 135373

Offset: 1

Author

Jonathan Vos Post, Dec 19 2007

Keywords

• nonn

Comments

This is to A000566 as A136117 is to A000326.

The sequence contains 12852 and 19751431167846, which are the smallest heptagonal numbers equal to twice another heptagonal number. - R. J. Mathar, Jan 13 2008

Examples

			Where hep(k) = k-th heptagonal number = A000566(k):
a(1) = 697 = hep(17) = 616 + 81 = hep(16) + hep(6).
a(2) = 3186 = hep(36) = 1782 + 1404 = hep(27) + hep(24).
a(3) = 3744 = hep(39) = 2673 + 1071 = hep(33) + hep(21).
a(4) = 5221 = hep(46) = 4347 + 874 = hep(42) + hep(19).
		

Links

• Eric Weisstein's World of Mathematics, Heptagonal Number.

Crossrefs

Cf. A000566, A136117.

Programs

Mathematica

Module[{nn=1000,heps},heps=Table[(n(5n-3))/2,{n,nn}]; Select[ Union[ Total/@ Tuples[Take[heps,nn/2],2]],MemberQ[heps,#]&]] (* Harvey P. Dale, Dec 18 2015 *)

Formula

{x such that x in A000566 and x = A000566(i) + A000566(j) for i, j > 0 and where A000566(k) = k*(5*k-3)/2}.

Extensions

More terms from R. J. Mathar, Jan 13 2008