

A049040


Number of Sophie Germain primes <= Prime[ 10^n ].


1




OFFSET

1,1


COMMENTS

Sophie Germain primes are primes p such that 2p+1 is also prime.


LINKS

Table of n, a(n) for n=1..8.
Index entries for sequences related to numbers of primes in various ranges


EXAMPLE

The first 10 primes are 2,3,5,7,11,13,17,23,29 and 31. 6 of these are Sophie Germain primes, namely: 2,3,5,11,23 and 29.


MATHEMATICA

<< NumberTheory`NumberTheoryFunctions`; cnt = 0; currentPrime = 1; For[ i = 1, i == i, i ++, currentPrime = NextPrime[ currentPrime ]; If[ PrimeQ[ 2*currentPrime + 1 ], cnt++ ]; If[ IntegerQ[ Log[ 10, i ] ], Print[ cnt ] ]; ]


CROSSREFS

Sequence in context: A144037 A187458 A100308 * A103649 A053946 A211946
Adjacent sequences: A049037 A049038 A049039 * A049041 A049042 A049043


KEYWORD

nonn


AUTHOR

Dennis S. Kluk (mathemagician(AT)ameritech.net)


EXTENSIONS

More terms from Alex Healy, Mar 19 2001


STATUS

approved



