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A152097
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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)=i-th Mersenne prime
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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| These are certified primes using PFGW from Primeform group
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EXAMPLE
| 3*2^1*(2^2-1)-1=17 prime as 19 so k(1)=1 as M(1)=2^2-1 3*2^1*(2^3-1)-1=41 prime as 43 so k(2)=1 as M(2)=2^3-1 3*2^2*(2^5-1)+1=373 prime so k(3)=2 as M(3)=2^5-1
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PROG
| Contribution from Michael B. Porter (michael_b_porter(AT)yahoo.com), Mar 18 2010: (Start)
(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^m-1), i=i-1)); 2^m-1}
A152097(n) = {local(k, m); k=1; m=mersenne(n); while(!(isprime(3*2^k*m-1)||isprime(3*2^k*m+1)), k=k+1); k} (End)
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CROSSREFS
| Cf. A145983.
Sequence in context: A131345 A134423 A061260 * A119442 A064861 A191528
Adjacent sequences: A152094 A152095 A152096 * A152098 A152099 A152100
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KEYWORD
| more,nonn
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AUTHOR
| Pierre CAMI (pierre-cami(AT)bbox.fr), Nov 24 2008
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