17672631899
domain: N
Appears in sequences
- a(n) = binomial(2n+1, n+1) - 1.at n=18A010763
- Number of 2n-bead black-white reversible strings with n black beads and fundamental period 2n.at n=19A045627
- Number of 2n-bead black-white complementable strings with n black beads and fundamental period 2n.at n=19A045630
- a(n) = |{(x_1, x_2, ... , x_n) : 1 <= x_1 <= x_2 <= ... <= x_n <= n, gcd(x_1, x_2, ... , x_n, n) = 1}|.at n=18A343565
- a(n) is the numerator of tanh(Sum_{k=1..n-1} artanh(k/n)), where artanh is the inverse hyperbolic tangent function.at n=18A382257