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 A213524 Numbers not representable as the sum of three octagonal numbers. 2
 4, 5, 6, 7, 11, 12, 13, 14, 15, 18, 19, 20, 25, 26, 27, 28, 31, 32, 33, 34, 35, 36, 38, 39, 44, 45, 46, 47, 51, 52, 53, 54, 55, 57, 58, 59, 60, 64, 68, 70, 71, 72, 75, 76, 77, 78, 79, 83, 84, 85, 89, 90, 91, 92, 93, 95, 99, 100, 102, 103, 108, 109, 110, 111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS There are an infinite number of numbers that are not the sum of three octagonal numbers. REFERENCES R. K. Guy, Unsolved Problems in Number Theory, D3. LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 R. K. Guy, Every number is expressible as the sum of how many polygonal numbers?, Amer. Math. Monthly 101 (1994), 169-172. MATHEMATICA nn = 100; oct = Table[n*(3*n-2), {n, 0, nn}]; t = Table[0, {oct[[-1]]}]; Do[n = oct[[i]] + oct[[j]] + oct[[k]]; If[n <= oct[[-1]], t[[n]] = 1], {i, nn}, {j, i, nn}, {k, j, nn}]; Flatten[Position[t, 0]] CROSSREFS Cf. A000567 (octagonal numbers). Cf. A118278, A118279. Sequence in context: A288737 A139448 A022561 * A047312 A191164 A004714 Adjacent sequences:  A213521 A213522 A213523 * A213525 A213526 A213527 KEYWORD nonn AUTHOR T. D. Noe, Jul 16 2012 STATUS approved

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Last modified November 29 03:58 EST 2021. Contains 349416 sequences. (Running on oeis4.)