Right-Aligned Number Triangle in Python

Beginner
⏱️ 7 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Nested Loops
Right-aligned number triangle output in Python with continuous values from 1

What You’ll Learn

How to print a right-aligned number triangle in Python where numbers increase continuously across rows (1, 2, 3, …).

You’ll learn a common technique: print leading blanks before printing numbers to create alignment.

⭐ Pattern Output

For rows = 5, the pattern looks like this:

Output
        1
      2  3
    4  5  6
  7  8  9 10
11 12 13 14 15
1

Complete Python Program

Use a counter k that increments only when a number is printed. Print blanks for positions before the triangle starts.

Python
rows = 5
k = 0

for i in range(1, rows + 1):
    for j in range(rows, 0, -1):
        if j > i:
            print("   ", end="")
        else:
            k += 1
            print(f"{k:2d} ", end="")
    print()

🧠 How It Works

1

Initialize the counter

k = 0 tracks the next number to print.

Setup
2

Outer loop (rows)

for i in range(1, rows + 1) builds each row of the triangle.

Row control
3

Inner loop (fixed width)

for j in range(rows, 0, -1) keeps each line the same width so alignment is consistent.

Alignment
4

Print blanks or numbers

If j > i, print blanks. Otherwise increment k and print it using fixed-width formatting.

Logic
=

Right-aligned triangle

Total numbers printed are 1+2+…+n = n(n+1)/2, so time complexity is O(n²) for n rows.

2

Variation — User Input Version

Let the user choose the number of rows at runtime:

Python
rows = int(input("Enter the number of rows: "))
k = 0

for i in range(1, rows + 1):
    for j in range(rows, 0, -1):
        if j > i:
            print("   ", end="")
        else:
            k += 1
            print(f"{k:2d} ", end="")
    print()

💡 Tips for Enhancement

Try These

  • Validate input (reject rows < 1) before printing
  • Change alignment by printing fewer or more leading blanks
  • Print zero-padded numbers using {k:02d} formatting
  • Print the same pattern left-aligned by skipping the blank-printing branch
  • Turn it into Floyd’s triangle by printing sequential numbers without right alignment

Avoid

  • Forgetting print() after each row
  • Not using fixed-width formatting (alignment will drift for 2+ digits)
  • Incrementing k even when printing blanks
  • Assuming user input is always valid (wrap int() if needed)

Key Takeaways

1

Print leading blanks to create right alignment.

2

Increment k only when you print a number to keep the sequence continuous.

3

Use fixed-width formatting ({k:2d}) so two-digit numbers align.

4

Total printed numbers are n(n+1)/2, giving O(n²) time.

❓ Frequently Asked Questions

Because once values reach two digits (10, 11, …), spacing changes. Using {k:2d} keeps columns aligned.
It prints 1+2+…+n = n(n+1)/2 numbers overall.
Yes—remove the blank-printing branch and just print numbers for j from 1 to i.
O(n²) for n rows, because the total printed count grows like a triangular number.

Explore More Python Number Patterns!

From pyramids to Floyd’s triangle and beyond—practice nested loops with progressively richer patterns.

All Number Patterns →
Did you know?

Right alignment is usually created by printing spaces first. When numbers become two digits, fixed-width formatting makes the pattern stay visually stable.

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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