Here is an example of pattern like

1 
2 3 
4 5 6 
7 8 9 10

Example :

public class NumberTriangleClass{
    public static void main(String args[]){
        int n=1;
        for(int i=1;i<5;i++){
            for(int j=1;j<=i;j++){
            System.out.print(n);

            n=n+1;
            }
            System.out.println();
        }
    }
}