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A114250
Number of Fermat pseudoprimes to bases 2, 3, 5 and 7 less than 10^n.
0
0, 0, 0, 0, 3, 19, 63, 175, 501, 1230, 3086, 7469, 18402, 44748, 109787, 269289, 668521, 1675317, 4236270
OFFSET
1,5
LINKS
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
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