OFFSET
1,2
FORMULA
a(n) ~ 10^n / (n log 10). - Charles R Greathouse IV, May 11 2012
MATHEMATICA
f[n_] := Length[Select[Range[10^n], PrimeQ[#] && !PrimeQ[2#+1] && !PrimeQ[4#+1]&]]; Table[f[n], {n, 7}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Enrique Pérez Herrero, May 09 2012
STATUS
approved