If sum of first 7 terms of an AP is 49and that of 17 terms is 289 find the sum of the first n terms

If sum of first 7 terms of an AP is 49and that of 17 terms is 289 find

1.	If sum of first 7 terms of an AP is 49and that of 17 terms is 289 find the sum of the first n terms
Answer» Sn=n2(square of n) (11+n)n