520831domain: NAppears in sequencesNumbers that are palindromic in bases 2 and 5.at n=8A182232Number of ways two L-tiles can be placed on an n X n square.at n=33A243645a(n) = Sum_{1 <= x_1, x_2, x_3, x_4 <= n} n/gcd(x_1, x_2, x_3, x_4, n).at n=13A372961