1845585domain: NAppears in sequencesa(n) = (25*n^4-120*n^3+209*n^2-108*n)/6.at n=27A006529Odd numbers taking exactly 21 steps to reach 15 in A086793.at n=6A119398a(0) = a(1) = 1 and a(n+2) = a(n+1) * (3*a(n+1) - 2*a(n)^2), n>=0.at n=5A144621Hankel transform of the ruler function A001511.at n=16A334910