40802189312domain: NAppears in sequencesNumbers k such that d(k)^4 divides k.at n=20A046756Numerator of 2n/v(n)^2, where v(1) = 0, v(2) = 1, and v(n) = v(n-1)/(n-2) + v(n-2) for n >= 3; limit of 2n/v(n)^2 is Pi.at n=18A239224