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A156702
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Numbers k such that k^2 - 1 == 0 (mod 24^2).
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2
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1, 127, 161, 287, 289, 415, 449, 575, 577, 703, 737, 863, 865, 991, 1025, 1151, 1153, 1279, 1313, 1439, 1441, 1567, 1601, 1727, 1729, 1855, 1889, 2015, 2017, 2143, 2177, 2303, 2305, 2431, 2465, 2591, 2593, 2719, 2753, 2879, 2881, 3007, 3041, 3167, 3169
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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a(n) = -36 + 27*(-1)^n + (4-4*i)*(-i)^n + (4+4*i)*i^n + 72*n. - Harvey P. Dale, Apr 25 2012
Sum_{n>=1} (-1)^(n+1)/a(n) = (cot(Pi/288) - tan(17*Pi/288))*Pi/288. - Amiram Eldar, Feb 26 2023
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MATHEMATICA
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LinearRecurrence[{1, 0, 0, 1, -1}, {1, 127, 161, 287, 289}, 50] (* Vincenzo Librandi, Feb 08 2012 *)
With[{c=24^2}, Select[Range[3200], Divisible[#^2-1, c]&]] (* Harvey P. Dale, Apr 25 2012 *)
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PROG
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(PARI) a(n)=n\4*288+[-1, 1, 127, 161][n%4+1]
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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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