191862

Appears in sequences

• Number of border edges in all noncrossing rooted trees on n nodes.at n=7A045722
• Numbers k such that phi(k) = sigma(core(k)) where phi(k) is the Euler totient function, sigma(k) the sum of divisors of k and core(k) the squarefree part of k (the smallest integer such that k*core(k) is a square).at n=16A069552
• Numbers n such that sigma(n) = 10*phi(n) (where sigma=A000203, phi=A000010).at n=19A171256
• Numbers k such that sigma(k) = psi(k) + phi(k).at n=25A389478