hmmm we use a sequence all 3 digit numbers divisible by 6 the first one is 102 (16*6) the biggest one is 996 (166*6)
so we find how many numbers there are because we know a nice summation formula that goes like this for a sequence that has a first term of a1 and the term we are summing to is an and there are n terms from a1 to an, the sum is n(a1+an)/2
so how many terms are there? 16*6 to 166*6 well, hmm 166-16=150 because these are multipules 151 terms (include the 16)
