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-# Arithmetic-Derivative
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+# Arithmetic Derivative
+
+Arithmetic derivative calculator using this simple formulas:
+* 0' = 1' = 0;
+* if n is a prime, n' = 1;
+* if n = ab  (a and b > 1), n' = a'b + ab'
+
+More about arithmetic derivative:
+https://en.wikipedia.org/wiki/Arithmetic_derivative