cp's OEIS Frontend

A291961 Numbers n > 1 such that 2^lambda(n) == 1 (mod n^2), where lambda(n) is the Carmichael lambda function (A002322).

%I A291961 #26 Sep 15 2017 11:55:51
%S A291961 1093,3279,3511,7651,10533,14209,17555,22953,31599,42627,45643,52665,
%T A291961 99463,136929,157995,228215,298389,410787,684645,2053935,3837523,
%U A291961 11512569,19187615,26862661,34537707,49887799,57562845,80587983,134313305,149663397,172688535,241763949,249438995,349214593,402939915,448990191,748316985,1047643779,1208819745,1746072965,2244950955,3142931337,5238218895
%N A291961 Numbers n > 1 such that 2^lambda(n) == 1 (mod n^2), where lambda(n) is the Carmichael lambda function (A002322).
%C A291961 An alternative generalization of Wieferich primes (A001220).
%C A291961 A subsequence of A077816, since the A002322(n)|A000010(n). The first 12 terms are common.
%C A291961 15714656685 (see A265630) is also a term. - _Michel Marcus_, Sep 14 2017
%t A291961 Select[Range[2, 100000], Divisible[2^CarmichaelLambda[#] - 1, #^2] &]
%o A291961 (PARI) isok(n) = Mod(2, n^2)^lcm(znstar(n)[2]) == 1; \\ _Michel Marcus_, Sep 11 2017
%Y A291961 Cf. A265630, A001220, A002322, A077816, A182297, A246503.
%K A291961 nonn
%O A291961 1,1
%A A291961 _Amiram Eldar_, Sep 06 2017
%E A291961 a(32)-a(36) from _Michel Marcus_, Sep 11 2017
%E A291961 a(37)-a(41) from _Michel Marcus_, Sep 12 2017
%E A291961 a(42)-a(43) from _Michel Marcus_, Sep 14 2017