Reverse Shifted Number Triangle in Python

Beginner
⏱️ 5 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Nested Loops
Reverse shifted number triangle output (5, 45, 345, 2345, 12345) in Python programming

What You’ll Learn

How to print a reverse shifted number triangle in Python using nested for loops. The first row prints just rows, then each next row starts one number earlier, building up to 1..rows.

This pattern is a great way to practice descending row control while printing an ascending sequence on each row.

⭐ Pattern Output

For rows = 5, the pattern looks like this:

Output
5
45
345
2345
12345
1

Complete Python Program

The outer loop chooses the start value (from rows down to 1). The inner loop prints from that start up to rows.

Python
rows = 5

for i in range(rows, 0, -1):
    for j in range(i, rows + 1):
        print(j, end="")
    print()

🧠 How It Works

1

Choose the row count

rows = 5 sets the maximum digit printed.

Setup
2

Outer loop (decreasing start)

for i in range(rows, 0, -1) selects the starting number for each row: 5, 4, 3, 2, 1.

Row control
3

Inner loop (print i..rows)

for j in range(i, rows + 1) prints numbers from the current start i up to rows using print(j, end="").

Number printing
4

New line

print() ends the row and moves to the next line.

Line break
=

Reverse shifted 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 decide the number of rows at runtime using input():

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

for i in range(rows, 0, -1):
    for j in range(i, rows + 1):
        print(j, end="")
    print()

💡 Tips for Enhancement

Try These

  • Validate input (reject rows < 1) before printing the pattern
  • Add spaces between numbers with print(j, end=" ")
  • Print the non-reverse shifted pattern by looping i upward (Program 2 style)
  • Right-align the triangle by printing leading spaces before each row
  • Replace numbers with letters to create alphabet versions

Avoid

  • Forgetting print() between rows
  • Mixing up the range() endpoints (stop value is exclusive)
  • Using negative or zero rows without validating input
  • Assuming user input is always valid (wrap int() conversion if needed)

Key Takeaways

1

The outer loop decreases the starting digit from rows down to 1.

2

The inner loop prints from the current start i up to rows.

3

Total printed digits follow the triangular number count: n(n+1)/2.

4

This pattern combines a descending outer loop with an ascending inner loop.

❓ Frequently Asked Questions

Because the starting number decreases each row (5, 4, 3, 2, 1) while the ending number stays at rows, so you print more digits each time.
Yes. Replace print(j, end="") with print(j, end=" "). For neat formatting, consider fixed-width formatting.
That’s the standard shifted triangle (Program 2): use an outer loop that counts up and an inner loop that prints from i to rows.
O(n²) for n rows: total prints are 1+2+…+n = n(n+1)/2.

Explore More Python Number Patterns!

Keep going to discover more number pattern programs and strengthen your loop skills.

All Number Patterns →
Did you know?

Patterns that print 1+2+…+n digits are tied to triangular numbers. That’s why many nested-loop patterns have O(n²) output size.

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.

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