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 A213523 Numbers not representable as the sum of three heptagonal numbers. 3
 4, 5, 6, 10, 11, 12, 13, 16, 17, 22, 23, 24, 27, 28, 29, 30, 31, 33, 38, 39, 40, 44, 45, 46, 47, 49, 50, 51, 58, 60, 61, 64, 65, 66, 67, 71, 72, 76, 77, 78, 79, 84, 85, 87, 92, 93, 94, 97, 98, 101, 103, 104, 105, 108, 109, 118, 121, 124, 125, 127, 129, 132 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It is conjectured that 1348 positive numbers are not the sum of three heptagonal numbers. REFERENCES R. K. Guy, Unsolved Problems in Number Theory, D3. LINKS T. D. Noe, Table of n, a(n) for n = 1..1348 R. K. Guy, Every number is expressible as the sum of how many polygonal numbers?, Amer. Math. Monthly 101 (1994), 169-172. MATHEMATICA nn = 350; hep = Table[n*(5*n-3)/2, {n, 0, nn}]; t = Table[0, {hep[[-1]]}]; Do[n = hep[[i]] + hep[[j]] + hep[[k]]; If[n <= hep[[-1]], t[[n]] = 1], {i, nn}, {j, i, nn}, {k, j, nn}]; Flatten[Position[t, 0]] CROSSREFS Cf. A000566 (heptagonal numbers). Cf. A118278, A118279. Sequence in context: A144022 A028280 A120520 * A246441 A026312 A070751 Adjacent sequences:  A213520 A213521 A213522 * A213524 A213525 A213526 KEYWORD nonn,fini AUTHOR T. D. Noe, Jul 16 2012 STATUS approved

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Last modified June 1 07:40 EDT 2020. Contains 334759 sequences. (Running on oeis4.)