A114248 - OEIS

%I #16 Feb 16 2025 08:32:59

%S 0,0,0,4,11,36,95,257,685,1747,4405,10601,25991,63589,156965,387971,

%T 973753,2471133,6340799

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

%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FermatPseudoprime.html">Fermat Pseudoprime</a>.

%H <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>.

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

%Y Cf. A083737.

%K nonn,more,changed

%O 1,4

%A _Eric W. Weisstein_, Nov 18 2005

%E a(9)-a(19) from _Amiram Eldar_, Apr 16 2022