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

Author

Pierre CAMI, May 24 2007

Keywords

• nonn

Examples

			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.
		

Links

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

Crossrefs

Cf. A130325, A130326.

Programs

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 *)

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