ExpIntegralE[n, z] == ((-z)^(n - 1) ExpIntegralE[1, z])/(n - 1)! - Sum[z^(k - 1)/Pochhammer[1 - n, k], {k, 1, n - 1}]/E^z /; Element[n, Integers] && n > 0

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2001-10-29