A395819 a(n) is the number of Fouvry primes (A073024) < 10^n.

0, 5, 48, 383, 3219, 27449, 238606, 2107196, 18852406, 170462497, 1555234548, 14297664923

Offset

1,2

Links

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

Étienne Fouvry, Théorème de Brun-Titchmarsh; application au théorème de Fermat, Inventiones mathematicae 79 (1985): 383-408.

Charles R Greathouse IV, Density of primes p where p-1 has a prime factor exceeding p^(2/3), question in mathoverflow; answer by Ofir Gorodetsky, Nov 08, 2023.

Example

   n         a(n)     A006880(n)     approximate ratio
                   primepi(10^n)     a(n)/primepi(10^n)
   1            0              4     0.00000
   2            5             25     0.20000
   3           48            168     0.28571
   4          383           1229     0.31164
   5         3219           9592     0.33559
   6        27449          78498     0.34968
   7       238606         664579     0.35903
   8      2107196        5761455     0.36574
   9     18852406       50847534     0.37076
  10    170462497      455052511     0.37460
  11   1555234548     4118054813     0.37766
  12  14297664923    37607912018     0.38018

Crossrefs

Cf. A073024, A006880.

Sequence in context: A359969 A215050 A268785 * A268736 A247769 A389337

Adjacent sequences: A395814 A395817 A395818 * A395820 A395823 A395824

Keyword

nonn,hard,more

Author

Hugo Pfoertner, May 07 2026

Status

approved