Any of the series of numbers (1, 3, 6, 10, 15, etc.) obtained by continued summation of the natural numbers 1, 2, 3, 4, 5, etc. Read more here: https://www.mathsisfun.com/algebra/triangular-numbers.html

TriangularNumbers.java

public class TriangularNumbers {
  
  public static void main(String[] args) {
    
    int n = 0;
    
    for (int i = 1; i <= 10; i++)
    	System.out.println(n += i);
    
  }
  
}