Untouchable numbers: Difference between revisions
Added C
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13863 to 100000
150232 to 1000000
</pre>
=={{header|C}}==
Run time around 17 seconds on my Core i7 machine.
<syntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <locale.h>
bool *primeSieve(int limit) {
int i, p;
limit++;
// True denotes composite, false denotes prime.
bool *c = calloc(limit, sizeof(bool)); // all false by default
c[0] = true;
c[1] = true;
for (i = 4; i < limit; i += 2) c[i] = true;
p = 3; // Start from 3.
while (true) {
int p2 = p * p;
if (p2 >= limit) break;
for (i = p2; i < limit; i += 2 * p) c[i] = true;
while (true) {
p += 2;
if (!c[p]) break;
}
}
return c;
}
int main() {
const int limit = 1000000;
int i, j, n, uc = 2, p = 10, m = 63, ul = 151000;
bool *c = primeSieve(limit);
n = m * limit + 1;
int *sumDivs = (int *)calloc(n, sizeof(int));
for (i = 1; i < n; ++i) {
for (j = i; j < n; j += i) sumDivs[j] += i;
}
bool *s = (bool *)calloc(n, sizeof(bool)); // all false
for (i = 1; i < n; ++i) {
int sum = sumDivs[i] - i; // proper divs sum
if (sum <= n) s[sum] = true;
}
free(sumDivs);
int *untouchable = (int *)malloc(ul * sizeof(int));
untouchable[0] = 2;
untouchable[1] = 5;
for (n = 6; n <= limit; n += 2) {
if (!s[n] && c[n-1] && c[n-3]) untouchable[uc++] = n;
}
setlocale(LC_NUMERIC, "");
printf("List of untouchable numbers <= 2,000:\n");
for (i = 0; i < uc; ++i) {
j = untouchable[i];
if (j > 2000) break;
printf("%'6d ", j);
if (!((i+1) % 10)) printf("\n");
}
printf("\n\n%'7d untouchable numbers were found <= 2,000\n", i);
for (i = 0; i < uc; ++i) {
j = untouchable[i];
if (j > p) {
printf("%'7d untouchable numbers were found <= %'9d\n", i, p);
p *= 10;
if (p == limit) break;
}
}
printf("%'7d untouchable numbers were found <= %'d\n", uc, limit);
free(c);
free(s);
free(untouchable);
return 0;
}</syntaxhighlight>
{{out}}
<pre>
List of untouchable numbers <= 2,000:
2 5 52 88 96 120 124 146 162 188
206 210 216 238 246 248 262 268 276 288
290 292 304 306 322 324 326 336 342 372
406 408 426 430 448 472 474 498 516 518
520 530 540 552 556 562 576 584 612 624
626 628 658 668 670 708 714 718 726 732
738 748 750 756 766 768 782 784 792 802
804 818 836 848 852 872 892 894 896 898
902 926 934 936 964 966 976 982 996 1,002
1,028 1,044 1,046 1,060 1,068 1,074 1,078 1,080 1,102 1,116
1,128 1,134 1,146 1,148 1,150 1,160 1,162 1,168 1,180 1,186
1,192 1,200 1,212 1,222 1,236 1,246 1,248 1,254 1,256 1,258
1,266 1,272 1,288 1,296 1,312 1,314 1,316 1,318 1,326 1,332
1,342 1,346 1,348 1,360 1,380 1,388 1,398 1,404 1,406 1,418
1,420 1,422 1,438 1,476 1,506 1,508 1,510 1,522 1,528 1,538
1,542 1,566 1,578 1,588 1,596 1,632 1,642 1,650 1,680 1,682
1,692 1,716 1,718 1,728 1,732 1,746 1,758 1,766 1,774 1,776
1,806 1,816 1,820 1,822 1,830 1,838 1,840 1,842 1,844 1,852
1,860 1,866 1,884 1,888 1,894 1,896 1,920 1,922 1,944 1,956
1,958 1,960 1,962 1,972 1,986 1,992
196 untouchable numbers were found <= 2,000
2 untouchable numbers were found <= 10
5 untouchable numbers were found <= 100
89 untouchable numbers were found <= 1,000
1,212 untouchable numbers were found <= 10,000
13,863 untouchable numbers were found <= 100,000
150,232 untouchable numbers were found <= 1,000,000
</pre>
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