The nth triangulat number is n*(n+1)/2
The 100th is 100*101/2 = 5050
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The 100th pentagonal number is 14950.
The Nth number is (3N - 1), so the 100th number is 299 .
100th
Oh, dude, finding the 99th triangle number is like, totally easy. You just use the formula n(n+1)/2, where n is the number of the triangle you want. So, for the 99th triangle number, you plug in 99 for n, do some quick math, and boom, you've got it!
Sum of numbers in a nth row can be determined using the formula 2^n. For the 100th row, the sum of numbers is found to be 2^100=1.2676506x10^30.