A130327 Least prime p such that 3*p*2^n-1 and 3*p*2^n+1 are twin primes.

2, 2, 5, 3, 5, 2, 11, 3, 19, 17, 5, 113, 59, 317, 331, 307, 241, 2, 829, 23, 149, 127, 11, 3023, 1091, 787, 971, 1523, 2741, 727, 1051, 227, 211, 727, 89, 1163, 71, 367, 1031, 577, 89, 1213, 1151, 3, 1021, 283, 2699, 4933, 59, 647, 709

Offset

0,1

Links

Pierre CAMI, Table of n, a(n) for n = 0..200

Example

3*2*2^0-1=5, 3*2*2^0+1=7: 5 and 7 are twin primes so for n=0 p=2.
3*2*2^1-1=11, 3*2*2^1+1=13: 11 and 13 are twin primes so for n=1 p=2.

Mathematica

lpp[n_]:=Module[{p=2}, While[!AllTrue[3p 2^n+{1, -1}, PrimeQ], p=NextPrime[p]]; p]; Array[lpp, 60, 0] (* Harvey P. Dale, May 13 2022 *)

Prog

(PARI) a(n) = my(p=2); while (!(isprime(q=3*p*2^n-1) && isprime(q+2)), p=nextprime(p+1)); p; \\ Michel Marcus, Sep 23 2019

Crossrefs

Cf. A130325, A130326.

Sequence in context: A128134 A157223 A174608 * A224361 A341443 A224166

Adjacent sequences: A130324 A130325 A130326 * A130328 A130329 A130330

Keyword

nonn

Author

Pierre CAMI, May 24 2007

Status

approved