Sum of 1 to 1: 1
Sum of 1 to 2: 3
Sum of 1 to 3: 6
Sum of 1 to 4: 10
Sum of 1 to 5: 15
Sum of 1 to 6: 21
Sum of 1 to 7: 28
Sum of 1 to 8: 36
Sum of 1 to 9: 45
Sum of 1 to 10: 55
Sum of 1 to 11: 66
Sum of 1 to 12: 78
Sum of 1 to 13: 91
Sum of 1 to 14: 105
Sum of 1 to 15: 120
Sum of 1 to 16: 136
Sum of 1 to 17: 153
Sum of 1 to 18: 171
Sum of 1 to 19: 190
Sum of 1 to 20: 210