Java Program to Print Right Pascal Triangle Number Pattern

Last updated: October 17, 2026Oct 17, 2026

In this program we print a right Pascal triangle of numbers: the rows grow from 1 to 1 2 3 4 5 and then shrink back to 1, which looks like a triangle pointing to the right.

Like every pattern program, it is built from nested loops: the outer loop picks the row, and the inner loops print what goes on that row.

1. The Pattern

For 5 rows the program prints:

Pattern

2. How the Program Works

Here is what each printed line is made of when numberOfRows is 5:

Line	Leading spaces	Printed after the spaces
1	0	1
2	0	1 2
3	0	1 2 3
4	0	1 2 3 4
5	0	1 2 3 4 5
6	0	1 2 3 4
7	0	1 2 3
8	0	1 2
9	0	1

Both parts print the numbers from 1 to row on each row.
Step 1 counts row up from 1 to numberOfRows.
Step 2 counts row down from numberOfRows - 1 to 1. It starts one row lower so the longest row is printed only once.
System.out.println() moves to the next line after each row.

3. Java Program

Pattern20.java

public class Pattern20 {
    public static void main(String[] args) {
        int numberOfRows = 5;

        // Step 1: rows get longer, up to numberOfRows numbers
        for (int row = 1; row <= numberOfRows; row++) {
            for (int column = 1; column <= row; column++) {
                System.out.print(column + " ");
            }
            System.out.println();
        }

        // Step 2: rows get shorter again, without repeating the longest row
        for (int row = numberOfRows - 1; row >= 1; row--) {
            for (int column = 1; column <= row; column++) {
                System.out.print(column + " ");
            }
            System.out.println();
        }
    }
}

Output

4. Print the Pattern for Any Number of Rows

To let the user choose the size of the pattern, read the number of rows with a Scanner. The loops stay the same.

Pattern20Input.java

import java.util.Scanner;

public class Pattern20Input {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of rows: ");
        int numberOfRows = scanner.nextInt();
        scanner.close();

        // Step 1: rows get longer, up to numberOfRows numbers
        for (int row = 1; row <= numberOfRows; row++) {
            for (int column = 1; column <= row; column++) {
                System.out.print(column + " ");
            }
            System.out.println();
        }

        // Step 2: rows get shorter again, without repeating the longest row
        for (int row = numberOfRows - 1; row >= 1; row--) {
            for (int column = 1; column <= row; column++) {
                System.out.print(column + " ");
            }
            System.out.println();
        }
    }
}

Output (with sample input)

Enter the number of rows: 4
1
1 2
1 2 3
1 2 3 4
1 2 3
1 2
1

5. Summary

The outer loop picks the row; the inner loops print the spaces and the numbers for that row.
Work out how many spaces and which numbers each row needs, then write one inner loop for each.
Keep numberOfRows in a variable, so the same program can print the pattern in any size.

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