octave:2> rat (0.13)
ans =

                          
0 + 1/(8 + 1/(-3 + 1/(-4)))

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>

static unsigned int fast_sqrt(unsigned int arg)
{
unsigned int one,res = 0;
for(one = 1UL << (sizeof(one)*8 - 2); one > arg; one >>=2);

while(one)
{
unsigned int k= res+one;
if(arg >= k)
{
arg -= k;
res += 2*one;
}
res >>= 1;
one >>= 2;
}
return res;
}

unsigned int factorize(unsigned int arg, unsigned int initial)
{
unsigned int j, limit = fast_sqrt(arg);
if(initial == 1) initial += 1;
for(j=initial; (j<=limit)&&(arg%j);++j);
return (j<=limit)?j:0;
}

void get_mpys(uint16_t *a, uint16_t *b, unsigned int num)
{
unsigned int koeff=1;
*a = *b = 1;
while(koeff)
{
unsigned int k = factorize(num,koeff);
if(k)
{
koeff = k;
num /= k;
}
else
{
k = num;
koeff = 0;
}

if(*a * k < 65536)
*a *= k;
else
{
if(*b * k < 65536)
*b *= k;
else
{
*a=*b=0;
return;
}
}
}
}

/*test*/
int main()
{
uint16_t xa,xb;
unsigned int nnn= 7200000/7;
get_mpys(&xa,&xb, nnn);
printf("numb %d a= %d b= %d a*b = %d\n",nnn,xa,xb,xa*xb);
return 0;
}

#include <math.h>
#include <stdlib.h>
#include <stdio.h>

const unsigned int FQz=24000000;//входная частота таймера.
const float erratum=.00001;//допустимая ошибка.
const unsigned int MAXLOAD=65535;
//unsigned int Fs; //требуемая для установки частота.


void calc(unsigned int Fs, unsigned int *ld1, unsigned int *ld2){
int delta1;
int delta2;
unsigned int ldt1;
unsigned int ldt2;
unsigned int mult=(unsigned int)floor(FQz/(Fs) + 0.5);// получим общее произведение делителя частоты
unsigned int ldx=mult/65535; if(ldx==0){++ldx;}; //возьмём нижнюю оценку для делителя 1.

*ld2=0;
delta2=FQz;// загрузим заведомо превыщающее оценку значение
int cnt=0;
while((ldx<sqrt(mult)))
{
ldt2=(unsigned int)floor( mult/ldx);
ldt1=(unsigned int)floor(mult/ldt2);
if ((ldt2<MAXLOAD)){
delta1=abs(FQz-Fs*ldt1*ldt2);
if(delta1>abs(FQz-Fs*ldt1*(ldt2+1))){
++ldt2;
delta1=abs(FQz-Fs*ldt1*ldt2);
}
if ((delta1<delta2)){//обновим пару делителей, при вновь найденной минимальной ошибке.
*ld1=ldt1;
*ld2=ldt2;
delta2=delta1;
};
if(delta1==0)break;//если найден идеальный результат- остановимся.
//if((float)delta1<erratum*FQz)break;//если найден подходящий результат- остановимся.
if((delta1<erratum*FQz)&&(cnt==0)){cnt=ldx;}//если найден подходящий результат- запомним.
};
++ldx;
};
printf("\nfs=%d; ld1=%u; ld2=%u; delta=%d; ldx=%i; cnt=%i", Fs, *ld1, *ld2, delta2, ldx, cnt );//чисто отладочный вывод
}

int main() {
unsigned int ld1;
unsigned int ld2;

for (int i=1; i<999;i++){
calc(i, &ld1, &ld2);
};
printf("This is SPARTA!\r\n");
}

unsigned int factorize(unsigned int arg, unsigned int initial)
{
unsigned int j, limit = fast_sqrt(arg);
if(initial == 1) initial += 1;
if(limit*limit < arg) limit +=1;
for(j=initial; (j<=limit)&&(arg%j);++j);
return (j<=limit)?j:0;
}

def prime_nums(N):
    return reduce( (lambda r,x: (r.difference_update(range(x*x,N,2*x)) or r)
        if (x in r) else r), range(3, int((N+1)**0.5+1), 2),
        set([2] + range(3,N,2)))
        
aList= prime_nums(256**2)
nprims=len(aList)
print "//found {0} prime numbers".format(nprims)
#create u32-bitmap
u32bmp=[]
u32bmp[:]= [0 for j in xrange(65536/32)]
#map to
for nn in aList:
    u32bmp[nn/32] |= 1 << (nn % 32)
print "static const uint32_t prime_set[]={"
col = 0
ss=''
for nn in u32bmp:
    print "0x%08X," % nn
print "};"

char isPrime(uint_least16_t num)
{
    return (prime_set[num/32] & (1<<(num & 31)))? 1:0;
}

unsigned int next_prim(unsigned int current)
{
   while(!isPrime(++current));
   return current;
}

unsigned int factorize(unsigned int arg, unsigned int initial)
{
  unsigned int j, limit = fast_sqrt(arg);
  if(initial == 1) initial += 1;
  if(limit*limit < arg) limit +=1;
  for(j=initial; (j<=limit)&&(arg%j); j=next_prim(j));
  return (j<=limit)?j:0;
}