login
A210684
Number of primes p < 10^n such that both 2*p+1 and 4*p+1 are composite.
1
0, 7, 101, 864, 7365, 63331, 554839, 4931118, 44339730, 402709395, 3687732409, 34007530868
OFFSET
1,2
FORMULA
a(n) = A006880(n) - A092816(n) - A182265(n) + 1.
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
STATUS
approved