Python Program to Print a Number Triangle Pattern
mediumNested loopsPython
The classic nested-loop pattern: the outer loop picks the row, the inner loop prints that row's numbers.
The question
Read n and print this pattern with n rows, numbers separated by a single space: 1 1 2 1 2 3 …
The code
program.py
n = int(input())
for i in range(1, n + 1):
for j in range(1, i + 1):
print(j, end=" ")
print()Input
5
Output
1 1 2 1 2 3 1 2 3 4 1 2 3 4 5
How it works
- 1The outer loop runs i = 1 to n — one row each.
- 2The inner loop prints 1 up to i, with end=" " so they stay on one line.
- 3An empty print() after the inner loop ends the row.
Common mistakes
- Printing i instead of j in the inner loop, which gives 1 / 2 2 / 3 3 3.
- Forgetting the empty print(), which puts every number on one long line.
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