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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
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).
Sequence in context: A189136 A116026 A115915 * A209887 A064801 A109825
KEYWORD
nonn,fini,nice
AUTHOR
EXTENSIONS
Corrected by T. D. Noe, Feb 14 2007
STATUS
approved

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Last modified April 17 04:22 EDT 2024. Contains 371756 sequences. (Running on oeis4.)