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 A007536 Numbers that are not the sum of 3 hexagonal numbers (probably finite). (Formerly M3244) 5
 4, 5, 9, 10, 11, 14, 19, 20, 23, 24, 25, 26, 32, 33, 37, 38, 39, 41, 42, 48, 50, 53, 54, 55, 59, 63, 64, 65, 69, 70, 76, 77, 80, 83, 85, 86, 89, 99, 102, 104, 108, 110, 113, 114, 115, 116, 123, 124, 128, 129, 130, 131, 140, 143, 144, 145, 146, 152, 161, 162, 167 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Jud McCranie remarks that a(638) = 146858 is probably the last term. REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS T. D. Noe, Table of n, a(n) for n=1..638 R. K. Guy, Every number is expressible as the sum of how many polygonal numbers?, Amer. Math. Monthly 101 (1994), 169-172. MATHEMATICA notSumQ[n_] := Reduce[0 <= x <= y <= z && n == x*(2x - 1) + y*(2y - 1) + z*(2z - 1), {x, y, z}, Integers] === False; A007536 = Reap[ Do[ If[notSumQ[n], Print[n]; Sow[n]], {n, 1, 135}]][[2, 1]] (* Jean-François Alcover, Jun 27 2012 *) PROG (MATLAB) N = 10^7; % to get all terms up to N M = floor((sqrt(1+8*N)+1)/4); H = zeros(1, N); H((1:M) .*(2*(1:M)-1)) = 1; H2 = conv(H, H); H2 = H2(1:N); H3 = conv(H, H2); HS = H(3:N) + H2(2:N-1) + H3(1:N-2); find(HS==0) + 2 % Robert Israel, Jul 06 2016 CROSSREFS Cf. A000384 (hexagonal numbers). Cf. A118278, A118279. Sequence in context: A189136 A116026 A115915 * A209887 A064801 A109825 Adjacent sequences:  A007533 A007534 A007535 * A007537 A007538 A007539 KEYWORD nonn,fini,nice AUTHOR EXTENSIONS Corrected by T. D. Noe, Feb 14 2007 STATUS approved

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Last modified August 9 11:08 EDT 2020. Contains 336323 sequences. (Running on oeis4.)