The first line is numbered 1, the second line is numbered 2, the third line is numbered 3, and so on. The number of digits in each row is equal to the number of rows. So the total number of 50 lines is (1+50)*50/2= 1275. The first line is 1, the second line from left to right is: 2,3, the third line is 4,5,6, and the fourth line is 7,8,9, 10. The size of the last number in the pyramid sequence actually represents the total number of numbers in the pyramid sequence. So the last number in line 50 is 1275.