1911 Encyclopædia Britannica/Number/Totients

26. Totients.—By the totient of , which is denoted, after Euler, by , we mean the number of integers prime to , and not exceeding . If , the numbers not exceeding and not prime to it are of which the number is : hence . If are prime to each other, ; and hence for the general case, if , where the product applies to all the different prime factors of . If , are the different divisors of ,

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For example, .