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A052968
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a(n) = 1 + 2^(n-1) + n for n > 0, a(0) = 2.
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7
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2, 3, 5, 8, 13, 22, 39, 72, 137, 266, 523, 1036, 2061, 4110, 8207, 16400, 32785, 65554, 131091, 262164, 524309, 1048598, 2097175, 4194328, 8388633, 16777242, 33554459, 67108892, 134217757, 268435486, 536870943, 1073741856, 2147483681
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OFFSET
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0,1
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COMMENTS
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O. M. Cain proves that the number of consecutive zeros in the decimal expansion of 5^(n+2^n+2), that is 5^a(n+1), is nondecreasing and grows to infinity as m gets bigger. See link. - Michel Marcus, Nov 07 2019
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LINKS
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FORMULA
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G.f.: (-2 + 5*x - 3*x^2 + x^3)/(-1+2*x)/(-1+x)^2
Recurrence: {a(3)=8, a(2)=5, a(1)=3, a(0)=2, 2*a(n)-a(n+1)-n=0}.
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MAPLE
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spec := [S, {S=Union(Sequence(Prod(Sequence(Z), Z)), Prod(Sequence(Z), Sequence(Z)))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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MATHEMATICA
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CoefficientList[Series[(-2+5*x-3*x^2+x^3)/(-1+2*x)/(-1+x)^2, {x, 0, 40}], x] (* Vincenzo Librandi, Jun 22 2012 *)
Join[{2}, Table[1+2^(n-1)+n, {n, 40}]] (* or *) LinearRecurrence[{4, -5, 2}, {2, 3, 5, 8}, 40] (* Harvey P. Dale, Feb 10 2018 *)
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PROG
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(Magma) I:=[2, 3, 5, 8]; [n le 4 select I[n] else 4*Self(n-1)-5*Self(n-2)+2*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Jun 22 2012
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
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STATUS
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approved
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