Question

The positive integers are arranged in a continuation of the pattern shown to the right. The value of the integer in the 72nd row (horizontal) and the 15th column (vertical) is 1 3 4 10 11
2 5 9 12
6 8 13 7 14 15

Answer 1

Answer:

first, note that the element at (72,15) is the 15th element along the diagonal starting at row 86, which starts at (86,1) and moves up to the right.

the even-numbered rows start with 1 + the previous odd-numbered row

The odd-numbered row n starts with the value n(n+1)/2

so the element at (86,1) is 1 + 85*86/2 = 3656

so the element at (72,15) is 3656 + 14 = 3670