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A182265
Number of primes p < 10^n such that 4*p+1 is also prime.
4
2, 9, 31, 176, 1057, 7422, 53709, 407198, 3198946, 25773602, 212205881, 1777532673
OFFSET
1,1
MATHEMATICA
f[n_] := Length[Select[Range[10^n], PrimeQ[#] && PrimeQ[4#+1]&]]; Table[f[n], {n, 7}]
PROG
(PARI) a(n)=my(s=0); forprime(p=2, 10^n, s+=isprime(4*p+1)); s \\ Charles R Greathouse IV, Apr 23 2012
CROSSREFS
Sequence in context: A150911 A150912 A165653 * A212873 A109770 A242512
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(10)-a(12) from Charles R Greathouse IV, Apr 23 2012
STATUS
approved