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 A213525 Numbers not representable as the sum of three 9-gonal numbers. 2
 4, 5, 6, 7, 8, 12, 13, 14, 15, 16, 17, 20, 21, 22, 23, 28, 29, 30, 31, 32, 35, 36, 37, 38, 39, 40, 41, 43, 44, 45, 50, 51, 52, 53, 54, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 73, 74, 78, 80, 81, 82, 83, 86, 87, 88, 89, 90, 91, 95, 96, 97, 98, 102, 103 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It is conjectured that 5282 positive numbers are not the sum of three 9-gonal numbers. REFERENCES R. K. Guy, Unsolved Problems in Number Theory, D3. LINKS T. D. Noe, Table of n, a(n) for n = 1..5282 R. K. Guy, Every number is expressible as the sum of how many polygonal numbers?, Amer. Math. Monthly 101 (1994), 169-172. MATHEMATICA nn = 700; non = Table[n*(7*n - 5)/2, {n, 0, nn}]; t = Table[0, {non[[-1]]}]; Do[n = non[[i]] + non[[j]] + non[[k]]; If[n <= non[[-1]], t[[n]] = 1], {i, nn}, {j, i, nn}, {k, j, nn}]; Flatten[Position[t, 0]] CROSSREFS Cf. A001106 (9-gonal numbers). Cf. A118278, A118279. Sequence in context: A161428 A285429 A073073 * A047567 A050038 A285218 Adjacent sequences:  A213522 A213523 A213524 * A213526 A213527 A213528 KEYWORD nonn,fini AUTHOR T. D. Noe, Jul 16 2012 STATUS approved

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Last modified December 3 20:35 EST 2021. Contains 349468 sequences. (Running on oeis4.)