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A260259
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a(n) = F(n)*F(n+1) - (-1)^n, where F = A000045.
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3
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-1, 2, 1, 7, 14, 41, 103, 274, 713, 1871, 4894, 12817, 33551, 87842, 229969, 602071, 1576238, 4126649, 10803703, 28284466, 74049689, 193864607, 507544126, 1328767777, 3478759199, 9107509826, 23843770273, 62423800999, 163427632718, 427859097161, 1120149658759
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OFFSET
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0,2
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COMMENTS
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Primes in sequence for n = 1, 3, 5, 6, 9, 24, 42, 48, 53, 71, 86, 102, 138, 182, 302, 438, 506, 926, ...
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LINKS
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FORMULA
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G.f.: (-1 + 4*x - x^2)/((1 + x)*(1 - 3*x + x^2)).
a(n) = -a(-n-1) = 2*a(n-1) + 2*a(n-2) - a(n-3) for all n in Z.
a(n) = F(n+2)^2 - 2*F(n+1)^2.
a(n) = A206351((n+2)/2)-2 for even n; a(n) = A003482((n-1)/2)+2 for odd n.
Sum_{i>=0} 1/a(i) = .754301907697893871765121109686...
a(n) = (2^(-1-n)*(-3*(-1)^n*2^(2+n)-(3-sqrt(5))^n*(-1+sqrt(5))+(1+sqrt(5))*(3+sqrt(5))^n))/5. - Colin Barker, Sep 29 2016
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MAPLE
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MATHEMATICA
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Table[Fibonacci[n] Fibonacci[n + 1] - (-1)^n, {n, 0, 30}]
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PROG
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(PARI) for(n=0, 30, print1(fibonacci(n)*fibonacci(n+1)-(-1)^n", "));
(PARI) a(n) = round((2^(-1-n)*(-3*(-1)^n*2^(2+n)-(3-sqrt(5))^n*(-1+sqrt(5))+(1+sqrt(5))*(3+sqrt(5))^n))/5) \\ Colin Barker, Sep 29 2016
(PARI) Vec(-(1-4*x+x^2)/((1+x)*(1-3*x+x^2)) + O(x^30)) \\ Colin Barker, Sep 29 2016
(Sage) [fibonacci(n)*fibonacci(n+1)-(-1)^n for n in (0..30)]
(Maxima) makelist(fib(n)*fib(n+1)-(-1)^n, n, 0, 30);
(Magma) [Fibonacci(n)*Fibonacci(n+1)-(-1)^n: n in [0..30]];
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CROSSREFS
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Cf. A226205: numbers of the form F(n)*F(n+1)+(-1)^n.
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KEYWORD
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sign,easy
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AUTHOR
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STATUS
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approved
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