The Fibonacci Sequence is the series of numbers:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

Each number in the sequence is found by adding up the two numbers before it:

• 1 (in the third position) is found by adding the two numbers before it (0+1),
• 2 is found by adding the two numbers before it (1+1)
• and so on until the limit or base case is reached

php recursive

function fibonacci($num){
  if ($num <= 1) return 1;
  else return (fibonacci($num - 1) + fibonacci($num - 2));
 }
for ($counter = 0; $counter < 20; $counter++){
  echo fibonacci($counter) . ' ';
}

Javascript recursive

function fibonacci(num) {
  if (num <= 1) return 1;
  return fibonacci(num - 1) + fibonacci(num - 2);
}
for (counter = 0; counter < 20; counter++){
  console.log(fibonacci(counter) + ' ');
}

php array

function fibonacci($num) {
  $fib = [0, 1];
  for($i=1; $i < $num; $i++) {
      $fib[] = $fib[$i] + $fib[$i-1];
  }
  return $fib;
}
print_r(fibonacci(20));

Javascript array

function fibonacci(num) {
  fib = [0, 1];
  for(i=1; i < num; i++) {
      fib.push(fib[i] + fib[i-1]);
  }
  return fib;
}
console.log(fibonacci(20));

php simple string

function fibonacci($num) {
  $num1 = 0;
  $num2 = 1;
  $counter = 0;
  while ($counter < $num) {
    echo $counter . ': ' . $num1 . " | ";
    $num3 = $num2 + $num1;
    $num1 = $num2;
    $num2 = $num3;
    $counter++;
  }
}
fibonacci(20);

Javascript simple string

function fibonacci(num) {
  let num1 = 0, num2 = 1, counter = 0, num3 = 0;
  while (counter < num){
    console.log(counter + ":" + num1);
    num3 = num2 + num1;
    num1 = num2;
    num2 = num3;
    counter++;
  }
}
fibonacci(20);