You can put this solution on YOUR website! This is an arithmetic sequence. Take note how we add 6 each time to generate the next term (eg: 7+6 = 13, 13+6 = 19, etc)
The common difference is therefore d = 6.
The first term is 7, so
The nth term is
So the sigma notation summation would be
Notice how plugging k = 1 leads to
6*k+1 = 6*1+1 = 7
which is the first term of the summation string "7+13+19+...+61"
while plugging k = 10 leads to
6*k+1 = 6*10+1 = 60+1 = 61
which is the last term of the summation string "7+13+19+...+61"
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