79397009999domain: NAppears in sequencesPseudoprime Chebyshev numbers: odd composite integers n such that T_n(a) == a (mod n) for all integers a, where T(x) is Chebyshev polynomial of first kind.at n=1A175530Composite squarefree numbers k such that for any prime p dividing k both (p-1)/2 and (p+1)/2 divide k+1.at n=7A392557