A182265 Number of primes p < 10^n such that 4*p+1 is also prime.

2, 9, 31, 176, 1057, 7422, 53709, 407198, 3198946, 25773602, 212205881, 1777532673

Offset

1,1

Links

Table of n, a(n) for n=1..12.

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

Cf. A023212, A092816.

Sequence in context: A150911 A150912 A165653 * A212873 A109770 A242512

Adjacent sequences: A182262 A182263 A182264 * A182266 A182267 A182268

Keyword

nonn

Author

Enrique Pérez Herrero, Apr 22 2012

Extensions

a(10)-a(12) from Charles R Greathouse IV, Apr 23 2012

Status

approved