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A118286
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Numbers n such that n=0 (mod 4) or n=2 (mod 12).
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0
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2, 4, 8, 12, 14, 16, 20, 24, 26, 28, 32, 36, 38, 40, 44, 48, 50, 52, 56, 60, 62, 64, 68, 72, 74, 76, 80, 84, 86, 88, 92, 96, 98, 100, 104, 108, 110, 112, 116, 120, 122, 124, 128, 132, 134, 136, 140, 144, 146, 148, 152, 156, 158, 160, 164, 168, 170, 172, 176, 180, 182
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Except for n=2, conjectured n such that A118278(n)=-1 and A118282(n)=-1; n such that there is an infinite set of numbers not representable as the sum of three n-gonal numbers or three generalized n-gonal numbers.
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (2,-2,2,-1)
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FORMULA
| G.f. 2*x*(1+2*x^2) / ( (x^2+1)*(x-1)^2 ). - R. J. Mathar, Dec 02 2011
a(n) = 2*A047237(n+1) = 3*n-1+cos(n*Pi/2). - R. J. Mathar, Dec 02 2011
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MATHEMATICA
| Union[4*Range[50], 2+12*Range[16]]
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CROSSREFS
| Sequence in context: A064657 A182837 A048314 * A024911 A024906 A160162
Adjacent sequences: A118283 A118284 A118285 * A118287 A118288 A118289
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KEYWORD
| nonn,easy
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Apr 23 2006
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