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A252943 Number of Fermat pseudoprimes to base 2 between 2^n and 2^(n+1) that are not Carmichael numbers.

%I A252943 #19 Mar 06 2023 07:59:57
%S A252943 0,0,0,0,0,0,0,1,1,3,3,5,10,12,14,21,31,41,64,100,127,165,216,288,397,
%T A252943 572,723,955,1344,1793,2399,3280,4228,5728,7738,10223,13895,18324,
%U A252943 24437,33007,43850,58173,77938,104689,139195,187497,252020,337731,452631,606942
%N A252943 Number of Fermat pseudoprimes to base 2 between 2^n and 2^(n+1) that are not Carmichael numbers.
%C A252943 This is a count, by power-of-two intervals, of the number of Fermat pseudoprimes that are not Carmichael numbers. A182490 contains the count of Carmichael numbers by power-of-two intervals.
%H A252943 Daniel Suteu, <a href="/A252943/b252943.txt">Table of n, a(n) for n = 1..63</a>
%H A252943 Jan Feitsma and William F. Galway, <a href="http://www.cecm.sfu.ca/Pseudoprimes/index-2-to-64.html">Tables of pseudoprimes and related data</a>.
%H A252943 R. G. E. Pinch, <a href="http://s369624816.websitehome.co.uk/rgep/psp-13.gz">Pseudoprimes up to 10^13</a>.
%o A252943 (Magma)
%o A252943 // Fermat pseudoprimes that are not Carmichael numbers,
%o A252943 // count by power of two intervals
%o A252943 for i:= 1 to 20 do
%o A252943   isum:=0;
%o A252943   for n:= 2^i + 1 to 2^(i+1) - 1 by 2 do
%o A252943      if (IsOne(2^(n-1) mod n)
%o A252943            and not IsPrime(n)
%o A252943            and not n mod CarmichaelLambda(n) eq 1)
%o A252943            then isum:=isum+1;
%o A252943      end if;
%o A252943   end for;
%o A252943   i,isum;
%o A252943 end for;
%Y A252943 Cf. A001567, A182490, A001567.
%K A252943 nonn
%O A252943 1,10
%A A252943 _Brad Clardy_, Dec 25 2014
%E A252943 a(21) from _Jon E. Schoenfield_, Dec 25 2014
%E A252943 a(22)-a(50) from _Daniel Suteu_, Mar 06 2023