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A133251
Heptagonal numbers A000566 which are the sum of two other heptagonal numbers > 0.
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
1,1
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
LINKS
Eric Weisstein's World of Mathematics, Heptagonal Number.
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}.
EXAMPLE
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).
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 *)
CROSSREFS
Sequence in context: A185377 A118059 A028500 * A243837 A116338 A293203
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Dec 19 2007
EXTENSIONS
More terms from R. J. Mathar, Jan 13 2008
STATUS
approved