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

1,5

Links

Table of n, a(n) for n=1..19.

Eric Weisstein's World of Mathematics, Fermat Pseudoprime.

Formula

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

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 *)

Crossrefs

Cf. A083739.

Sequence in context: A370434 A041015 A185448 * A249994 A339401 A316601

Adjacent sequences: A114247 A114248 A114249 * A114251 A114252 A114253

Keyword

nonn,more

Author

Eric W. Weisstein, Nov 18 2005

Extensions

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

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

Status

approved