BetaRegularized[z, a, b] == 1 - (((1 - z)^b z^a)/(b Beta[a, b])) Sum[((-1)^k Pochhammer[a + b, k] (z - 1)^k)/Pochhammer[1 + b, k], {k, 0, Infinity}] /; Abs[z - 1] < 1 && !(Element[-b, Integers] && -b >= 0)

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2001-10-29