89235domain: NAppears in sequencesa(n) is the maximal difference between two distinct n-digit numbers with the property that when one of them is typed into a calculator and rotated 180 degrees, the other one is seen.at n=4A125520Number of (w,x,y,z) with all terms in {1,...,n} and w^2>=x^2+y^2+z^2.at n=29A212095