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%I #9 Dec 15 2019 08:36:40
%S 140,1054,1068,4844,11209,19856,24949,28390,78184,423796,769516,
%T 4283544,5935168,13116053,122189752,441252296,528500308,636697392,
%U 669629030,669778082,1228748591
%N Composite numbers k such that 2^(k-1) == - lambda(k) (mod k), where lambda is the Carmichael lambda function (A002322).
%C Composite numbers k such that A062173(k) = A277127(k).
%C The odd terms are 11209, 24949, 13116053, ...
%C Note that if p is an odd prime, then 2^(p-1) == - lambda(p) (mod p), because lambda(p) = p-1.
%e 140 is a term since it is composite and 2^(140-1) == 140 - lambda(140) == 128 (mod 140).
%t Select[Range[10^6], CompositeQ[#] && PowerMod[2, # - 1, #] == # - CarmichaelLambda[#] &]
%Y Cf. A002322, A062173, A277127.
%K nonn,more
%O 1,1
%A _Amiram Eldar_ and _Thomas Ordowski_, Dec 15 2019