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A169727
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a(n) = 3*(2^(n+1)-2)*(2^(n+1)-1) + 1.
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8
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1, 19, 127, 631, 2791, 11719, 48007, 194311, 781831, 3136519, 12564487, 50294791, 201252871, 805158919, 3220930567, 12884312071, 51538427911, 206156070919, 824629002247, 3298525446151, 13194120658951, 52776520384519, 211106157035527, 844424779137031
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OFFSET
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0,2
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COMMENTS
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A subsequence of the centered hexagonal numbers A003215.
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LINKS
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FORMULA
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a(n) = 7*a(n-1) - 14*a(n-2) + 8*a(n-3).
G.f.: -(1+12*x+8*x^2) / ( (x-1)*(2*x-1)*(4*x-1) ). (End)
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MATHEMATICA
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CoefficientList[Series[-(1 + 12*x + 8*x^2)/((x-1)*(2*x-1)*(4*x-1)), {x, 0, 30}], x](* Vincenzo Librandi, Dec 03 2012 *)
LinearRecurrence[{7, -14, 8}, {1, 19, 127}, 30] (* Harvey P. Dale, Jan 15 2015 *)
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PROG
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(Magma) I:=[1, 19, 127]; [n le 3 select I[n] else 7*Self(n-1) -14*Self(n-2) +8*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Dec 03 2012
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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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Alice V. Kleeva (alice27353(AT)gmail.com), Jan 19 2010
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EXTENSIONS
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STATUS
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approved
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