21266

Appears in sequences

• Numerators of continued fraction convergents to sqrt(209).at n=6A041388
• Numbers k such that the number of prime divisors of the k-th Catalan number (counted with multiplicity) divides k.at n=31A121612
• Number of right triangles on a (n+1)X9 grid.at n=11A189813
• Total number of distinct sequences for the number of double occupancy in the underlying Fermion problem (see comment), i.e., the number of distinct hopping sequences (cf. A198761, A225823) in four-colored rooted trees with n nodes, starting and ending with the same coloring in two colors (cf. A198760, corresponding to zero double-occupancy).at n=6A240605
• Numbers m such that the GCD of the x's that satisfy sigma(x) = m is 4.at n=23A241649
• Integers, a, which are the solutions to the equation a^2 + b^3 = c^4, with integers a, b > 0, and indexed off of A242183.at n=29A242184
• Numbers k such that sopfr(k + sopfr(k)) = sopfr(k) + sopfr(sopfr(k)), where sopfr = A001414.at n=26A376851