Count all 3-digit numbers, that are divisable by 3, that can be formed by using digits {1,2,3,4,5,6} (the digits can repeat)

count.js

let div = document.getElementById('result');

let nmap = {};

function append(str) {
 if (nmap[str]) return;

 div.innerHTML += str;
 nmap[str] = true;
}

function test(a,b,c) {
 if ((a + b + c) % 3 == 0 ) {
   append(a+''+b+''+c+', ');
 }
}

for (let a = 1; a < 7; a++) {
	for (let b = 1; b < 7; b++) {
    for (let c = 1; c < 7; c++) {
			test(a,b,c);
      test(a,c,b);
      
      test(b,a,c);
      test(b,c,a);
      
      test(c,a,b);
      test(c,b,a);
    }
	}
}

append("total: "+Object.keys(nmap).length);