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A181490
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Numbers k such that 3*2^k-1 and 3*2^k+1 are twin primes (A001097).
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9
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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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MAPLE
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a:=k->`if`(isprime(3*2^k-1) and isprime(3*2^k+1), k, NULL); seq(a(k), k=1..1000); # Muniru A Asiru, Mar 11 2018
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MATHEMATICA
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fQ[n_] := PrimeQ[3*2^n - 1] && PrimeQ[3*2^n + 1]; k = 1; lst= {}; While[k < 15001, If[fQ@k, AppendTo[lst, k]; Print@k]; k++ ] (* Robert G. Wilson v, Nov 05 2010 *)
Select[Range[20], AllTrue[3*2^#+{1, -1}, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Sep 24 2014 *)
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PROG
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(PARI) for( k=1, 999, ispseudoprime(3<<k-1)||next; ispseudoprime(3<<k+1)&print(k))
(GAP) Filtered([1..300], k->IsPrime(3*2^k-1) and IsPrime(3*2^k+1)); # Muniru A Asiru, Mar 11 2018
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CROSSREFS
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KEYWORD
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bref,hard,more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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