Pan base non-primes: Difference between revisions
Added C solution
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Number odd = 161 or 16.894019%
Number even = 792 or 83.105981%
</pre>
=={{header|C}}==
<syntaxhighlight lang="c">#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
bool is_prime(uint64_t n) {
if (n < 2)
return false;
if (n % 2 == 0)
return n == 2;
if (n % 3 == 0)
return n == 3;
if (n % 5 == 0)
return n == 5;
static const uint64_t wheel[] = {4, 2, 4, 2, 4, 6, 2, 6};
for (uint64_t p = 7;;) {
for (int i = 0; i < 8; ++i) {
if (p * p > n)
return true;
if (n % p == 0)
return false;
p += wheel[i];
}
}
}
// Compute the digits of n in base 10, least significant digit first.
int digits(uint64_t n, uint8_t* d, int size) {
int count = 0;
for (; n > 0 && size > 0; n /= 10, --size, ++count)
*d++ = n % 10;
return count;
}
// Convert digits in the given base to a number (least significant digit first).
uint64_t from_digits(uint8_t* a, int count, uint64_t base) {
uint64_t n = 0;
while (count-- > 0)
n = n * base + a[count];
return n;
}
#define MAX_DIGITS 20
bool is_pan_base_non_prime(uint64_t n) {
if (n < 10)
return !is_prime(n);
if (n > 10 && n % 10 == 0)
return true;
uint8_t d[MAX_DIGITS];
int count = digits(n, d, MAX_DIGITS);
uint8_t max_digit = 0;
for (int i = 0; i < count; ++i) {
if (max_digit < d[i])
max_digit = d[i];
}
for (uint64_t base = max_digit + 1; base <= n; ++base) {
if (is_prime(from_digits(d, count, base)))
return false;
}
return true;
}
int main() {
printf("First 50 prime pan-base composites:\n");
int count = 0;
for (uint64_t n = 2; count < 50; ++n) {
if (is_pan_base_non_prime(n)) {
++count;
printf("%3llu%c", n, count % 10 == 0 ? '\n' : ' ');
}
}
printf("\nFirst 20 odd prime pan-base composites:\n");
count = 0;
for (uint64_t n = 3; count < 20; n += 2) {
if (is_pan_base_non_prime(n)) {
++count;
printf("%3llu%c", n, count % 10 == 0 ? '\n' : ' ');
}
}
const uint64_t limit = 10000;
int odd = 0;
count = 0;
for (uint64_t n = 2; n <= limit; ++n) {
if (is_pan_base_non_prime(n)) {
++count;
if (n % 2 == 1)
++odd;
}
}
printf("\nCount of pan-base composites up to and including %llu: %d\n",
limit, count);
double percent = 100.0 * odd / count;
printf("Percent odd up to and including %llu: %f\n", limit, percent);
printf("Percent even up to and including %llu: %f\n", limit,
100.0 - percent);
return 0;
}</syntaxhighlight>
{{out}}
<pre>
First 50 prime pan-base composites:
4 6 8 9 20 22 24 26 28 30
33 36 39 40 42 44 46 48 50 55
60 62 63 64 66 68 69 70 77 80
82 84 86 88 90 93 96 99 100 110
112 114 116 118 120 121 130 132 134 136
First 20 odd prime pan-base composites:
9 33 39 55 63 69 77 93 99 121
143 165 169 187 231 253 273 275 297 299
Count of pan-base composites up to and including 10000: 3849
Percent odd up to and including 10000: 18.030657
Percent even up to and including 10000: 81.969343
</pre>
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