2097480domain: NAppears in sequencesa(n) = Sum_{d|n} phi(d)*2^(n/d).at n=21A053635a(n) = Sum_{odd d|n} phi(d)*2^(n/d).at n=21A053636a(n) = Sum_{d|n} 2^d*phi(2*n/d).at n=20A306898Numbers k such that k + 1, 2k + 1, 3k + 1, 4k + 1, and 6k + 1 are all prime.at n=31A333721