Question 137342
Your series looks like
1st term : 16=16=16+9(1-1)
2nd term : 25=16+9=16+9(2-1)
3rd term : 34=16+9+9=16+9(3-1)
4th term : 43=16+9+9+9=16+9(4-1)
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30th term : 261=16+9(29)=16+9(30-1)
The sum of all those terms would be then the sum of 30*16 since there are 30 sixteens added plus 9 times the sum from 1 to 29.
The sum from 1 to n equals n(n+1)/2.
The sum from 1 to 29 equals 29(30)/2=435.
The total sum is then 30*16 (480) plus 9*435 (3915) and equals 4395.