Let S_n =1/2+1/6+1/12+1/20+… upto n terms. If the sum of the first six terms of an A.P. with first term -p and common difference p is √(2026 S_2025),…

Let $\displaystyle \mathrm{S}_{\mathrm{n}}=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\ldots$ upto n terms. If the sum of the first six terms of an A.P. with first term -p and common difference p is $\displaystyle \sqrt{2026 \mathrm{~S}_{2025}}$, then the absolute difference betwen $\displaystyle 20^{\text {th }}$ and $\displaystyle 15^{\text {th }}$ terms of the A.P. is