PHP Number Triangle Pattern (Starting from 11)

What Is This Pattern?

An increasing number triangle from 11 prints $i values on row $i, each computed as 9 + $i + $j — so the first cell is always 11.

Rule: for i from 1 to rows
        for j from 1 to i
          print (9 + i + j) and a space

11
12 13
13 14 15
14 15 16 17
15 16 17 18 19     ← rows = 5

Follows the number-star diamond in Program 31; next is the same shape starting from 1 in Program 33.

How to Solve It

Outer loop grows $i. Inner loop prints $i values with the formula 9 + $i + $j, separated by spaces.

Pseudocode

for i from 1 to rows:
    for j from 1 to i:
        print (9 + i + j) and a space
    print newline

Cheat sheet

Printing Numbers vs Starting a New Line

Print values without a newline, then end the row once.

Live Preview

Change the row count and the increasing triangle updates instantly — capped at 9 for readable demos.

11 
12 13 
13 14 15 
14 15 16 17 
15 16 17 18 19 

Worked Walkthrough — $rows = 5

Trace how each ($i, $j) pair maps to 9 + $i + $j.

Total numbers = 1 + 2 + … + n = n(n+1)/2 → O(n²).

PHP Programs

Three complete programs: fixed $rows = 5, custom base with CLI input, and a compact $rows = 3 demo. Use View Output to reveal sample results.

<?php
for ($i = 1; $i <= 5; $i++) {
    for ($j = 1; $j <= $i; $j++) {
        echo (9 + $i + $j) . " ";
    }
    echo PHP_EOL;
}
?>

11 
12 13 
13 14 15 
14 15 16 17 
15 16 17 18 19 

<?php
echo "Enter rows: ";
$rowsInput = trim(fgets(STDIN));

if (!is_numeric($rowsInput) || (int) $rowsInput <= 0) {
    echo "Please enter a positive integer." . PHP_EOL;
    exit(1);
}

echo "Enter base: ";
$baseInput = trim(fgets(STDIN));

if (!is_numeric($baseInput)) {
    echo "Please enter a whole number." . PHP_EOL;
    exit(1);
}

$rows = (int) $rowsInput;
$baseVal = (int) $baseInput;

for ($i = 1; $i <= $rows; $i++) {
    for ($j = 1; $j <= $i; $j++) {
        echo ($baseVal + $i + $j) . " ";
    }
    echo PHP_EOL;
}
?>

Enter rows: 3
Enter base: 9
11 
12 13 
13 14 15 

if (!is_numeric($rowsInput) || (int) $rowsInput < 1 || (int) $rowsInput > 9) {
    echo "Enter a whole number from 1 to 9." . PHP_EOL;
    exit(1);
}

<?php
$rows = 3;

for ($i = 1; $i <= $rows; $i++) {
    for ($j = 1; $j <= $i; $j++) {
        echo (9 + $i + $j) . " ";
    }
    echo PHP_EOL;
}
?>

11 
12 13 
13 14 15 

Time and Space Complexity

Row $i prints i numbers. Total = 1 + 2 + … + n = n(n+1)/2 → O(n²) time. Only a few loop variables are needed.

Key Takeaways