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A155097
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Numbers k such that k^2 == -1 (mod 37).
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6
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6, 31, 43, 68, 80, 105, 117, 142, 154, 179, 191, 216, 228, 253, 265, 290, 302, 327, 339, 364, 376, 401, 413, 438, 450, 475, 487, 512, 524, 549, 561, 586, 598, 623, 635, 660, 672, 697, 709, 734, 746, 771, 783, 808, 820, 845, 857, 882, 894, 919, 931, 956, 968
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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a(n) = 6*(-1)^(n+1) + 37*floor(n/2).
a(2k+1) = 37*k + a(1), a(2k) = 37*k - a(1), with a(1) = A002314(5) since 37 = A002144(5).
a(n) = a(n-2) + 37 for all n > 2. (End)
Sum_{n>=1} (-1)^(n+1)/a(n) = cot(6*Pi/37)*Pi/37. - Amiram Eldar, Feb 26 2023
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MATHEMATICA
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Select[Range[1000], PowerMod[#, 2, 37]==36&] (* Harvey P. Dale, May 06 2012 *)
CoefficientList[Series[(6 + 25 x + 6 x^2)/((1 + x) (1 - x)^2), {x, 0, 30}], x] (* Vincenzo Librandi, May 03 2014 *)
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PROG
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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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Terms checked, a(28) corrected, and minor edits by M. F. Hasler, Jun 16 2010
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STATUS
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approved
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