A114250 Number of Fermat pseudoprimes to bases 2, 3, 5 and 7 less than 10^n.

0, 0, 0, 0, 3, 19, 63, 175, 501, 1230, 3086, 7469, 18402, 44748, 109787, 269289, 668521, 1675317, 4236270

Offset: 1

Author

Eric W. Weisstein, Nov 18 2005

Keywords

• nonn
• more

Links

• Eric Weisstein's World of Mathematics, Fermat Pseudoprime.

Crossrefs

Cf. A083739.

Programs

Mathematica

Table[Count[Select[Range[2, 10^6], ! PrimeQ[#] && PowerMod[2, # - 1, #] == 1 && PowerMod[3, # - 1, #] == 1 && PowerMod[5, # - 1, #] == 1 && PowerMod[7, # - 1, #] == 1 &], x_ /; x < 10^n], {n, 6}]  (* Robert Price, Jun 09 2019 *)

Formula

a(n) = card{ m in A083739, m<10^n}. - R. J. Mathar, Feb 07 2008

Extensions

a(9)-a(12) from Amiram Eldar, Sep 18 2021

a(13)-a(19) from Amiram Eldar, Apr 22 2022