

A152097


Least k(n) such that 3*2^k(n)*M(n)1 or 3*2^k(n)*M(n)+1 is prime (or both primes) with M(i)=ith Mersenne prime.


1



1, 1, 2, 1, 3, 2, 1, 5, 6, 9, 31, 44, 18, 71, 81, 1097, 64, 789, 42, 17, 908, 722, 1500, 1496, 5690, 6720, 3340, 18768, 9597, 13835
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OFFSET

1,3


COMMENTS

These are certified primes using PFGW from Primeform group.


LINKS

Table of n, a(n) for n=1..30.


EXAMPLE

3*2^1*(2^2  1)  1 = 17 is prime, as is 19, so k(1)=1 as M(1) = 2^2  1;
3*2^1*(2^3  1)  1 = 41 is prime, as is 43, so k(2)=1 as M(2) = 2^3  1;
3*2^2*(2^5  1) + 1 = 373 is prime, so k(3)=2 as M(3) = 2^5  1.


PROG

(PARI) /* these functions are too slow for n > about 15 */
mersenne(n) = {local(i, m); i=n; m=1; while(i>0, m=m+1; if(isprime(2^m1), i=i1)); 2^m1}
A152097(n) = {local(k, m); k=1; m=mersenne(n); while(!(isprime(3*2^k*m1)isprime(3*2^k*m+1)), k=k+1); k} \\ Michael B. Porter, Mar 18 2010


CROSSREFS

Cf. A145983.
Sequence in context: A131345 A134423 A061260 * A119442 A064861 A305299
Adjacent sequences: A152094 A152095 A152096 * A152098 A152099 A152100


KEYWORD

more,nonn


AUTHOR

Pierre CAMI, Nov 24 2008


STATUS

approved



