18673200domain: NAppears in sequencesa(n) is the number of sets of natural numbers [a,b,c,d,e] that can be produced with the numbers [0..n] such that the values of all the distinct parenthesized expressions of a-b-c-d-e are different.at n=29A054026Numbers k such that phi(k+1) = 5*phi(k).at n=1A201253