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A245179
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Numbers of the form 2^k+3 or 3*2^k+1, k >= 2.
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2
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7, 11, 13, 19, 25, 35, 49, 67, 97, 131, 193, 259, 385, 515, 769, 1027, 1537, 2051, 3073, 4099, 6145, 8195, 12289, 16387, 24577, 32771, 49153, 65539, 98305, 131075, 196609, 262147, 393217, 524291, 786433, 1048579, 1572865, 2097155, 3145729, 4194307, 6291457
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OFFSET
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1,1
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COMMENTS
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Numbers whose binary expansion is 10..011 or 110..01.
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LINKS
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FORMULA
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a(n) = 3*a(n-2)-2*a(n-4). G.f.: -x*(14*x^3+8*x^2-11*x-7) / ((x-1)*(x+1)*(2*x^2-1)). - Colin Barker, Jul 19 2014
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MATHEMATICA
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CoefficientList[Series[- (14 x^3 + 8 x^2 - 11 x - 7)/((x - 1) (x + 1) (2 x^2 - 1)), {x, 0, 50}], x] (* Vincenzo Librandi, Jul 23 2014 *)
LinearRecurrence[{0, 3, 0, -2}, {7, 11, 13, 19}, 50] (* Harvey P. Dale, Mar 05 2015 *)
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PROG
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(Magma) &cat [[3*2^i+1, 2^(i+2)+3]: i in [1..30]]; // Bruno Berselli, Jul 23 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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STATUS
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approved
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