Number Pattern 39 in PHP

Beginner
⏱️ 6 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Nested Loops
PHP Number Pattern 39 output (12345, 23451, 34521, 45321, 54321)

What You’ll Learn

How to print Number Pattern 39 in PHP using nested loops. Each row is made of two parts: an ascending sequence from $i to $n, followed by a descending sequence from $i-1 to 1.

This creates rows like 23451 and 45321.

⭐ Pattern Output

For $n = 5, the pattern looks like this:

Output
12345
23451
34521
45321
54321
1

Complete PHP Program

First print $i..$n, then print $i-1..1 to complete the row.

PHP
<?php
$n = 5;

for ($i = 1; $i <= $n; $i++) {
    for ($j = $i; $j <= $n; $j++) {
        echo $j;
    }
    for ($k = $i; $k > 1; $k--) {
        echo $k - 1;
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Choose the maximum number

$n = 5; defines the range of digits and the number of rows.

Setup
2

Outer loop (rows)

for ($i = 1; $i <= $n; $i++) controls the starting digit for each row.

Row control
3

First half: print $i..$n

for ($j = $i; $j <= $n; $j++) prints ascending digits from the row start.

Ascending part
4

Second half: print $i-1..1

for ($k = $i; $k > 1; $k--) prints the wrap-around tail to complete the row.

Descending part
=

Two-part row construction

Each row prints exactly n digits, and over n rows that leads to O(n²) work.

2

Variation — User Input (CLI) Version

Let the user decide $n at runtime using standard input (run from terminal with php):

PHP
<?php
echo "Enter n: ";
$n = (int) trim(fgets(STDIN));

if ($n < 1) {
    exit("n must be at least 1." . PHP_EOL);
}

for ($i = 1; $i <= $n; $i++) {
    for ($j = $i; $j <= $n; $j++) {
        echo $j;
    }
    for ($k = $i; $k > 1; $k--) {
        echo $k - 1;
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Replace digits with letters to generate a similar alphabet pattern
  • Add spaces between digits for readability (for example, print $j . " ")
  • Generate the same row using arrays, then join and print once
  • Start from a different base by changing the outer loop range
  • Reverse the output order (print rows from $n down to 1)

Avoid

  • Using invalid $n without input validation
  • Mixing row/column logic (outer loop should control rows)
  • Assuming output stays identical if you add separators
  • Forgetting the newline after each row

Key Takeaways

1

Each row is built from two runs: $i..$n then $i-1..1.

2

Every row prints exactly $n digits.

3

The pattern scales by changing only $n.

4

Total work is O(n²).

❓ Frequently Asked Questions

For $i=3, the first loop prints 345. The second loop prints 21. Combined, the row is 34521.
It’s a simple two-part construction that looks like a rotation because values wrap from $n back to 1.
Print a space after each digit, e.g. echo $j . " ";. The pattern remains the same, but the formatting changes.
O(n²) because you print n digits for each of n rows.

Explore More PHP Number Patterns!

Try more rotation and wrap-around patterns to strengthen your loop thinking.

All Number Patterns →
Did you know?

Each row contains all numbers from 1 to $n exactly once—just in a different order.

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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