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A010002
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a(0) = 1, a(n) = 9*n^2 + 2 for n>0.
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2
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1, 11, 38, 83, 146, 227, 326, 443, 578, 731, 902, 1091, 1298, 1523, 1766, 2027, 2306, 2603, 2918, 3251, 3602, 3971, 4358, 4763, 5186, 5627, 6086, 6563, 7058, 7571, 8102, 8651, 9218, 9803, 10406, 11027, 11666, 12323, 12998, 13691, 14402, 15131, 15878, 16643
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OFFSET
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0,2
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COMMENTS
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Apart from the first term, numbers of the form (r^2+2*s^2)*n^2+2 = (r*n)^2+(s*n-1)^2+(s*n+1)^2: in this case is r=1, s=2. After 1, all terms are in A000408. [Bruno Berselli, Feb 06 2012]
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LINKS
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FORMULA
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Sum_{n>=0} 1/a(n) = 3/4+sqrt(2)/12 *Pi*coth(Pi/3*sqrt 2) = 1.1606262038.. - R. J. Mathar, May 07 2024
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MATHEMATICA
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Join[{1}, LinearRecurrence[{3, -3, 1}, {11, 38, 83}, 50]] (* Vincenzo Librandi, Aug 03 2015 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy,changed
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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