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A053604
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Number of ways to write n as an ordered sum of 3 nonzero triangular numbers.
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16
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0, 0, 0, 1, 0, 3, 0, 3, 3, 1, 6, 0, 6, 3, 6, 3, 3, 9, 1, 12, 0, 6, 9, 6, 6, 6, 9, 6, 12, 0, 10, 9, 12, 6, 9, 9, 3, 18, 3, 12, 12, 9, 9, 9, 12, 10, 12, 9, 9, 18, 6, 6, 27, 6, 12, 6, 9, 18, 15, 15, 6, 21, 9, 13, 12, 9, 18, 21, 9, 6, 21, 15, 15, 15, 12, 15, 18, 15, 9
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OFFSET
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0,6
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COMMENTS
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Fermat asserted that every number is the sum of three triangular numbers. This was proved by Gauss, who recorded in his Tagebuch entry for Jul 10 1796 that: EYPHEKA! num = DELTA + DELTA + DELTA.
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REFERENCES
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Mel Nathanson, Additive Number Theory: The Classical Bases, Graduate Texts in Mathematics, Volume 165, Springer-Verlag, 1996. See Chapter 1.
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LINKS
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FORMULA
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MATHEMATICA
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Table[a[n], {n, 0, nmax}]; Clear[counts];
counts[m_] :=
counts[m] = (Clear[a]; a[_] = 0;
Do[s = i*(i + 1)/2 + j*(j + 1)/2 + k*(k + 1)/2;
a[s] = a[s] + 1, {i, 1, m}, {j, 1, m}, {k, 1, m}];
A053603); counts[m = m0]; counts[m = 2*m]; While[
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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