Periodic minimum in the count of binomial coefficients not divisible by a prime

The summatory function of the number of binomial coefficients not divisible by a prime is known to exhibit regular periodic oscillations, yet identifying the less regularly behaved minimum of the underlying periodic functions has been open for almost all cases. We propose an approach to identify such minimum in some generality, solving particularly a previous conjecture of B. Wilson Asymptotic behavior of Pascal's triangle modulo a prime, Acta Arith. 83 (1998), pp. 105-116.