D[Erfc[z], {z, n}] == Erfc[z] KroneckerDelta[n] - Boole[n != 0, (((n - 1)!/(2^n Sqrt[Pi])) Sum[((-1)^(k - 1) 2^(2 k) z^(2 k - n - 1))/((2 k - n - 1)! (n - k)!), {k, 1, n}])/E^z^2] /; Element[n, Integers] && n >= 0

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2001-10-29