A265630 -id:A265630 - 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).

1093, 3279, 3511, 7651, 10533, 14209, 17555, 22953, 31599, 42627, 45643, 52665, 99463, 136929, 157995, 228215, 298389, 410787, 684645, 2053935, 3837523, 11512569, 19187615, 26862661, 34537707, 49887799, 57562845, 80587983, 134313305, 149663397, 172688535, 241763949, 249438995, 349214593, 402939915, 448990191, 748316985, 1047643779, 1208819745, 1746072965, 2244950955, 3142931337, 5238218895

Offset: 1

Amiram Eldar, Sep 06 2017

nonn

An alternative generalization of Wieferich primes (A001220).
A subsequence of A077816, since the A002322(n)|A000010(n). The first 12 terms are common.
15714656685 (see A265630) is also a term. - Michel Marcus, Sep 14 2017

Cf. A265630, A001220, A002322, A077816, A182297, A246503.

Select[Range[2, 100000], Divisible[2^CarmichaelLambda[#] - 1, #^2] &]

isok(n) = Mod(2, n^2)^lcm(znstar(n)[2]) == 1; \\ Michel Marcus, Sep 11 2017

a(32)-a(36) from Michel Marcus, Sep 11 2017
a(37)-a(41) from Michel Marcus, Sep 12 2017
a(42)-a(43) from Michel Marcus, Sep 14 2017

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).

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