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A156718
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Numbers k such that k^2 == -1 (mod 13^2).
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4
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70, 99, 239, 268, 408, 437, 577, 606, 746, 775, 915, 944, 1084, 1113, 1253, 1282, 1422, 1451, 1591, 1620, 1760, 1789, 1929, 1958, 2098, 2127, 2267, 2296, 2436, 2465, 2605, 2634, 2774, 2803, 2943, 2972, 3112, 3141, 3281, 3310, 3450, 3479, 3619, 3648, 3788
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OFFSET
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1,1
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COMMENTS
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Also, numbers of the form 169k +- 70.
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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).
Sum_{n>=1} (-1)^(n+1)/a(n) = tan(29*Pi/338)*Pi/169. - Amiram Eldar, Feb 26 2023
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MATHEMATICA
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LinearRecurrence[{1, 1, -1}, {70, 99, 239}, 50]
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PROG
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(Magma) [Floor(n/2)*169-70*(-1)^n: n in [1..50]];
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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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STATUS
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approved
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