A114246 Number of Fermat pseudoprimes to bases 2 and 3 less than 10^n.

0, 0, 0, 7, 23, 66, 187, 485, 1272, 3270, 8139, 20015, 50090, 125284, 318729, 813380, 2104139, 5514763, 14627441

Offset: 1

Author

Eric W. Weisstein, Nov 18 2005

Keywords

• nonn
• more

Links

• Eric Weisstein's World of Mathematics, Fermat Pseudoprime.
• Index entries for sequences related to pseudoprimes.

Crossrefs

Cf. A052155.

Programs

Mathematica

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

PARI

my(n=1, i=0); forcomposite(k=1, 1e20, if(Mod(2, k)^(k-1)==1 && Mod(3, k)^(k-1)==1, i++); if(k==10^n, print1(i, ", "); n++)) \\ Felix Fröhlich, Oct 11 2015

Extensions

a(9) from Felix Fröhlich, Oct 11 2015

a(10)-a(11) from Amiram Eldar, Sep 18 2021

a(12)-a(19) from Amiram Eldar, Apr 22 2022