smc

Question

Given the sets of consecutive integers 1,2, 3,4,5,6,7,8,9,10,; ;, where each set contains one more element than the preceding one, and where the first element of each set is one more than the last element of the preceding set. Let S_n be the sum of the elements in the nth set. Then S_21 equals:

Accepted Answer

The last element of the 21st set is 21 222=231, and hence the first element of the 21st set is 211. So S_21=231 2322-210 2112=4641, hence our answer is 4641