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A113422
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a(n)=[(5n^2+1)/3].
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0
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0, 2, 7, 15, 27, 42, 60, 82, 107, 135, 167, 202, 240, 282, 327, 375, 427, 482, 540, 602, 667, 735, 807, 882, 960, 1042, 1127, 1215, 1307, 1402, 1500, 1602, 1707, 1815, 1927, 2042, 2160, 2282, 2407, 2535, 2667, 2802, 2940, 3082, 3227, 3375, 3527, 3682, 3840
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| If n<a(m) then all integer solutions (i,j,k) of 2*i^2+2*j^2+3*k^2-2*i*k=n satisfy max(|i|,|j|,|k|)<m.
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FORMULA
| G.f.: (2x+3x^2+3x^3+2x^4)/((1-x)^2(1-x^3)). a(-n)=a(n). a(3n)=15n^2, a(3n+1)=15n^2+10n+2.
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PROG
| (PARI) a(n)=(5*n^2+1)\3
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CROSSREFS
| Sequence in context: A029888 A194112 A005449 * A061802 A003452 A000148
Adjacent sequences: A113419 A113420 A113421 * A113423 A113424 A113425
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KEYWORD
| nonn
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AUTHOR
| Michael Somos, Oct 31 2005
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