S is the sum of the first 20 terms of the series 3 + 4 + 6 + 9 + 13..... The value of S is

The sum of the first five terms of the series 3 +4 1/2+6 3/4+...=

Find the sum of first n terms of the series 1.3 + 2.5 + 3.7 + 4.9 +…..

Find the sum of first n terms of the series, 4+5+8+13+20+…

The sum of the first n terms of a series is 31, and the sum of the first n - 1 terms of the series is 20. What is the value of nth terms in the series?

Find sum of first 10 terms of geometric series 3,9, 27,……

Find the sum to n terms of the series 1 *2 *3 + 2*4*6 + 3*6*9+...

The difference between the sum of the first k terms of the series 1^3+2^3+3^3++n^3 and the sum of the first k terms of 1+2+3++ni s1980. The value of k is __________.

The sum of the first 20 terms common between the series 3+7+11+15+....1+6+11+16+.... and is