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A047495
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Numbers that are congruent to {2, 4, 5, 7} mod 8.
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1
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2, 4, 5, 7, 10, 12, 13, 15, 18, 20, 21, 23, 26, 28, 29, 31, 34, 36, 37, 39, 42, 44, 45, 47, 50, 52, 53, 55, 58, 60, 61, 63, 66, 68, 69, 71, 74, 76, 77, 79, 82, 84, 85, 87, 90, 92, 93, 95, 98, 100, 101, 103, 106, 108, 109, 111, 114, 116, 117, 119, 122, 124
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OFFSET
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1,1
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LINKS
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FORMULA
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G.f.: x*(2+x^2+x^3) / ( (x^2+1)*(x-1)^2 ). - R. J. Mathar, Nov 06 2015
a(n) = 2*a(n-1) - 2*a(n-2) + 2*a(n-3) - a(n-4) for n>4.
a(n) = (1+i)*(4*n-4*n*i+i-1+i^(1-n)-i^n)/4 where i=sqrt(-1).
E.g.f.: (2 + sin(x) - cos(x) + (4*x - 1)*exp(x))/2. - Ilya Gutkovskiy, May 27 2016
Sum_{n>=1} (-1)^(n+1)/a(n) = 3*Pi/16 - (sqrt(2)-1)*log(2)/8 + sqrt(2)*log(2-sqrt(2))/4. - Amiram Eldar, Dec 25 2021
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MAPLE
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MATHEMATICA
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Table[(1+I)*(4n-4n*I+I-1+I^(1-n)-I^n)/4, {n, 80}] (* Wesley Ivan Hurt, May 27 2016 *)
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PROG
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(Magma) [n : n in [0..150] | n mod 8 in [2, 4, 5, 7]]; // Wesley Ivan Hurt, May 27 2016
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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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