259207domain: NAppears in sequencesQuasi-Carmichael numbers to base 7: squarefree composites n such that (n,2*3*5) = 1 and prime p|n ==> p-7|n-7.at n=24A029556a(n) = a(n-1) + a(n-2) + a(n-3) with a(0)=2, a(1)=1, a(2)=2.at n=21A214899Cardinality of Image^inf({ 2 }) under repeated base-n zero-split doubling.at n=31A254638