Why do we reset the code in the first one, but not in the second one, and why in the second code there are values ​​of 100 twice, what is their essence?

Question

JavaScript

function printNumbersInterval() {
  var i = 1;
  var timerId = setInterval(function() {
    console.log(i);
    if (i == 20) clearInterval(timerId);
    i++;
  }, 100);
}

// вызов
printNumbersInterval();

function printNumbersTimeout20_100() {
  var i = 1;
  var timerId = setTimeout(function go() {
    console.log(i);
    if (i < 20) setTimeout(go, 100);
    i++;
  }, 100);
}

// вызов
printNumbersTimeout20_100()