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 A181490 Numbers k such that 3*2^k-1 and 3*2^k+1 are twin primes (A001097). 8
 1, 2, 6, 18 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sequences A181491 and A181492 list the corresponding primes. No more terms below three million. - Charles R Greathouse IV, Mar 14 2011 Intersection of A002235 and A002253. - Jeppe Stig Nielsen, Mar 05 2018 LINKS FORMULA Equals { k | A007283(k) in A014574 } = { k | A153893(k) in A001359 }. MAPLE 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 MATHEMATICA 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 *) PROG (PARI) for( k=1, 999, ispseudoprime(3<IsPrime(3*2^k-1) and IsPrime(3*2^k+1)); # Muniru A Asiru, Mar 11 2018 CROSSREFS Cf. A001097, A001359, A002235, A002253, A006512, A014574, A294730. Sequence in context: A264761 A253882 A183757 * A165325 A316765 A097635 Adjacent sequences:  A181487 A181488 A181489 * A181491 A181492 A181493 KEYWORD bref,nonn AUTHOR M. F. Hasler, Oct 30 2010 EXTENSIONS Pari program repaired by Charles R Greathouse IV, Mar 14 2011 STATUS approved

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Last modified April 21 20:03 EDT 2019. Contains 322328 sequences. (Running on oeis4.)