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/* factor - print the prime factors of a number Author: Andy Tanenbaum */ main(argc, argv) int argc; char *argv[]; { /* Factor a number */ long i, n, flag = 0, first(), atol(); if (argc != 2 || (n = atol(argv[1])) < 2) { printf("Usage: factor n (2 <= n < 2**31)\n"); exit(1); } if (n == 2) { printf("2 is a prime\n"); exit(0); } while (1) { i = first(n); if (i == 0) { if (flag == 0) printf("%ld is a prime\n", n); else printf("%ld\n", n); exit(0); } printf("%ld ", i); n = n / i; flag = 1; } } long first(k) long k; { /* Return the first factor of k. If it is a prime, return 0; */ long i; if (k == 2) return(0); if (k % 2 == 0) return (2); for (i = 3; i <= k / 3; i += 2) if (k % i == 0) return(i); return(0); }
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