1048817domain: NAppears in sequencesDuplicate of A029561.at n=9A028893Quasi-Carmichael numbers to base 2: squarefree composites n such that prime p|n ==> p-2|n-2.at n=9A029561a(n) = Sum_{d|n} d*2^(n/d - 1).at n=21A054599a(n) = Sum_{d|n, d odd} d*2^(n/d - 1), a(0)=0.at n=21A054601