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A047306
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Numbers that are congruent to {0, 2, 3, 4, 5, 6} mod 7.
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2
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0, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75, 76, 77
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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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G.f.: x^2*(2+x+x^2+x^3+x^4+x^5) / ( (1+x)*(1+x+x^2)*(x^2-x+1)*(x-1)^2 ). - R. J. Mathar, Oct 25 2011
a(n) = a(n-1) + a(n-6) - a(n-7) for n>7.
a(n) = n + floor((n-2)/6). (End)
a(n) = (42*n-27+3*cos(n*Pi)-12*cos(n*Pi/3)-4*sqrt(3)*sin(2*n*Pi/3))/36.
a(6k) = 7k-1, a(6k-1) = 7k-2, a(6k-2) = 7k-3, a(6k-3) = 7k-4, a(6k-4) = 7k-5, a(6k-5) = 7k-7. (End)
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MAPLE
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MATHEMATICA
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Select[Range[0, 100], MemberQ[{0, 2, 3, 4, 5, 6}, Mod[#, 7]] &] (* Vincenzo Librandi, Oct 22 2014 *)
LinearRecurrence[{1, 0, 0, 0, 0, 1, -1}, {0, 2, 3, 4, 5, 6, 7}, 70] (* Harvey P. Dale, May 28 2018 *)
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PROG
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(PARI) concat(0, Vec(x^2*(2+x+x^2+x^3+x^4+x^5)/((1+x)*(1+x+x^2)*(x^2-x+1)*(x-1)^2) + O(x^30))) \\ Michel Marcus, Oct 22 2014
(Magma) [n: n in [0..100] | n mod 7 in [0] cat [2..6]]; // Vincenzo Librandi, Oct 22 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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