19187615

Appears in sequences

• Numbers n > 1 such that 2^m == 1 (mod n^2), where m = A002326((n-1)/2).at n=21A265630
• Numbers n > 1 such that 2^lambda(n) == 1 (mod n^2), where lambda(n) is the Carmichael lambda function (A002322).at n=22A291961