find the nth triangular number in php

main.php
T_n = 1 + 2 + 3 + ... + n
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main.php
function nth_triangular_number($n) {

  // initialize sum to 0
  $sum = 0;

  // add up the numbers from 1 to n
  for ($i = 1; $i <= $n; $i++) {
    $sum += $i;
  }

  // return the nth triangular number
  return $sum;
}
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main.php
// find the 10th triangular number
$triangular_10 = nth_triangular_number(10);
echo "The 10th triangular number is: " . $triangular_10; // Output: The 10th triangular number is: 55
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