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A155450
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Numbers congruent to 5 or 18 mod 23.
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6
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5, 18, 28, 41, 51, 64, 74, 87, 97, 110, 120, 133, 143, 156, 166, 179, 189, 202, 212, 225, 235, 248, 258, 271, 281, 294, 304, 317, 327, 340, 350, 363, 373, 386, 396, 409, 419, 432, 442, 455, 465, 478, 488, 501, 511, 524, 534, 547, 557, 570, 580, 593, 603, 616
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OFFSET
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1,1
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COMMENTS
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Or, numbers n such that n^2 == 2 mod 23.
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LINKS
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FORMULA
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a(n) = a(n-1)+a(n-2)-a(n-3), with a(1)=5, a(2)=18, a(3)=28.
Sum_{n>=1} (-1)^(n+1)/a(n) = cot(5*Pi/23)*Pi/23. - Amiram Eldar, Feb 26 2023
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MATHEMATICA
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CoefficientList[Series[(5 + 13 x + 5 x^2)/((1 + x) (1 - x)^2), {x, 0, 60}], x] (* Vincenzo Librandi, May 03 2014 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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