is not in gosper.org/facfun.pdf because I couldn't relieve Product[BarnesG[-(i/n) + z], {i, 0, -1 + n}] == E^(((-1 + n^2)*Zeta'[-1])/n)* n^(BernoulliB[2, 1 + n*(-2 + z)]/(2*n))* BarnesG[2 + n*(-2 + z)]^(1/n)* (n*(-2 + z))!^(2 - 1/n - z)* Product[(-2 - i/n + z)!^(-1 - i/n + z), {i, 0, -1 + n}] of the explicit Product. And it requires branch diddling for "inexact" z. (If lhs is positive, just Abs the rhs.) But it's still useful. --rwg