Number of n-digit binary strings such that for all 2 <= k <= n, the string formed by the first k digits of the original string is composed of at least one-quarter 1's and one-quarter 0's.

A268691

Number of n-digit binary strings such that for all 2 <= k <= n, the string formed by the first k digits of the original string is composed of at least one-quarter 1's and one-quarter 0's.