A055550 - OEIS

%I #23 Jun 10 2019 00:45:32

%S 0,0,3,22,78,245,750,2057,5597,14884,38975,101629,264239,687007,

%T 1801533,4744920,12604009,33763684,91210364

%N Number of Poulet numbers (or pseudoprimes to base 2, A001567) less than 10^n.

%D J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 245, pp 68, Ellipses, Paris 2008. - _Lekraj Beedassy_, Jul 20 2008

%H Jan Feitsma and William Galway, <a href="http://www.cecm.sfu.ca/Pseudoprimes/index-2-to-64.html">Tables of pseudoprimes and related data</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PouletNumber.html">Poulet Number</a>

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

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

%Y Cf. A001567, A055552.

%K nonn,more

%O 1,3

%A _Eric W. Weisstein_

%E a(14) and a(15) computed by William F. Galway and communicated by Arthur Livingstone (arthur.livingstone(AT)gmail.com), Apr 10 2007

%E Edited by _N. J. A. Sloane_, Feb 01 2009 at the suggestion of _Charles R Greathouse IV_

%E a(14)-a(15) recomputed (were missing) and a(16)-a(19) added by _Charles R Greathouse IV_, Jan 28 2011, based on the calculations of Jan Feitsma