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A211397
Number of Sophie Germain primes less than 2^n.
2
0, 2, 3, 4, 6, 8, 11, 18, 26, 39, 62, 103, 170, 281, 474, 834, 1464, 2555, 4493, 8051, 14499, 26375, 48024, 88175, 161833, 297544, 549330, 1018008, 1893255, 3527324, 6588118, 12334363, 23140567, 43497488, 81930886, 154587025, 292149120
OFFSET
1,2
MATHEMATICA
nmax = 37; stable = Table[0, {nmax}];
Do[s = 0;
Do[If[And[PrimeQ[i], PrimeQ[2 i + 1]], s++], {i, 1, 2^n - 1}];
Print[n, " ", s]; stable[[n]] = s, {n, 1, nmax}];
stable (* Paul D. Beale, Sep 19 2014 *)
PROG
(PARI) a211397(n) = {local(r, i); r=0; for(i=1, 2^n-1, if(isprime(i)&&isprime(2*i+1), r=r+1)); r}
CROSSREFS
Sequence in context: A054782 A261082 A271487 * A173542 A323383 A329905
KEYWORD
nonn
AUTHOR
Michael B. Porter, Feb 08 2013
EXTENSIONS
a(30)-a(37) from Paul D. Beale, Sep 19 2014
STATUS
approved