Originally Posted by

**john.c**
But I guess code is secret now.

Still brute force, and the code isn't secret, just not that well written or interesting. Here's the most interesting bit:

Code:

struct Factor {
uint64_t factor;
uint64_t power;
};
struct Factor_List {
uint32_t used;
struct Factor factors[64]; // Any more than 64 unique factors means the number is way more than 2^64
};
int main(int argc, char *argv[])
{
find_primes(1000000000);
struct Factor_List fl1,fl2;
int limit = 125;
uint64_t a = 2;
uint64_t b = 3;
find_factors(a/2, &fl1); // Remove the factor of 2 from 'a'
while(a < 1000000000) {
int factors;
find_factors(b, &fl2);
factors = count_factors(&fl1,&fl2);
if(factors > limit) {
printf("The %ldth triangular number %ld has %d factors\n", a, a*(a+1)/2, factors);
while(limit < factors)
limit *= 2;
}
a+= 2;
find_factors(a/2, &fl1); // Remove the factor of 2 from 'a'
factors = count_factors(&fl1,&fl2);
if(factors > limit) {
printf("The %ldth triangular number %ld has %d factors\n", b, b*(b+1)/2, factors);
while(limit < factors)
limit *= 2;
}
b+= 2;
}
}