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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 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A000566, A136117. Sequence in context: A185377 A118059 A028500 * A243837 A116338 A293203 Adjacent sequences:  A133248 A133249 A133250 * A133252 A133253 A133254 KEYWORD nonn AUTHOR Jonathan Vos Post, Dec 19 2007 EXTENSIONS More terms from R. J. Mathar, Jan 13 2008 STATUS approved

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Last modified September 19 15:09 EDT 2020. Contains 337178 sequences. (Running on oeis4.)