171238

Appears in sequences

• Floor[X/Y] where X = concatenation of (n+1)-st odd number through the 2n-th odd number and Y = concatenation of first n odd numbers.at n=10A067093
• G.f.: Sum_{n>=0} x^n / (1-x)^(2*n+1) * [Sum_{k=0..n} C(n,k)^2 * x^k] * [Sum_{k=0..n} C(n,k)^2 * 2^k * x^k].at n=8A243948
• Number of parity-alternating permutations of [n] avoiding the pattern 321.at n=20A354208