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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <math.h>
  4.  
  5. // this is a program to find the first triangular number that is divisible by 500 factors
  6.  
  7. int main()
  8. {
  9.     long long int b = 0;        // limit for triangular num (1+2+3+......+b)
  10.     long long int d;            // divisor
  11.     long long int t = 0;        // triangular number in use
  12.     long long int r = 0;        // root of current test number
  13.     int f = 0;                  // factor counter
  14.  
  15.     while (f <= 500)
  16.     {
  17.         f = 0;
  18.  
  19.         // next triangular number
  20.         t += ++b;
  21.  
  22.         // get closest root.
  23.         r = floor(sqrt(t));
  24.  
  25.         // counts factors
  26.         for( d = 1 ; d < r; ++d )
  27.         {
  28.             if( t % d == 0 )
  29.                 f += 2;
  30.         }
  31.         if (t % r == 0)
  32.             ++f;
  33.     }
  34.  
  35.     printf("%lld is the first triangular number with more than 500 factors\n", t);
  36.     return 0;
  37. }
Success #stdin #stdout 1.71s 2248KB
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76576500 is the first triangular number with more than 500 factors
https://ideone.com/HdF0nQ
language:
C99 (gcc 8.3)
created:
11 years ago
visibility:
secret

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