Run results for: sum 3,5 dividents

Run details:

User agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 YaBrowser/17.3.1.840 Yowser/2.5 Safari/537.36

Browser: Yandex Browser 17

Operating system: Windows 7

Device Platform: Other

Date tested: 7 years ago

Test name	Executions per second
bu	903181.0 Ops/sec
ku	1809783.9 Ops/sec

Script Preparation code:

 var input = 214;
  function bu (N) {
    var q = Math.floor(N/3),
      w = Math.floor(N/5),
      e = Math.floor(N/15),
  
      A = q * (q+1) * 3 / 2,
      B = w * (w+1) * 5 / 2,
      AB = e * (e+1) * 15 / 2;
  
    return A + B - AB;
  }
  
  function ku (N) {
    var n3 = 3,
      n5 = 5,
      sum = 0;
  
    for (var i = 0; n3 <= N; n3 += 3, n5 += 5 * (1 + i % 2), ++i) {
      sum += n3;
  
      if (n5 < N) {
        sum += n5;
      }
    }
  }

Tests:

bu
bu(input);
ku
ku(input);