153912domain: NAppears in sequencesNumber of key permutations of length n: permutations {a_i} with |a_i - a_{i-1}| = 1 or 2.at n=27A003274Numbers x such that sigma(x)=sigma(V(x)), where sigma(x) is the sum of the divisors of x and V(x) the transform defined in A245252.at n=26A245469