Let for $n =1,2, \ldots \ldots, 50, S _{ a }$ be the sum of the infinite geometric progression whose first term is $n ^{2}$ and whose common ratio is $\frac{1}{(n+1)^{2}}$. Then the value of $\frac{1}{26}+\sum\limits_{n=1}^{50}\left(S_{n}+\frac{2}{n+1}-n-1\right)$ is equal to
$41600$
$47651$
$41651$
$41671$
Insert two numbers between $3$ and $81$ so that the resulting sequence is $G.P.$
$0.5737373...... = $
Fifth term of a $G.P.$ is $2$, then the product of its $9$ terms is
If the third term of a $G.P.$ is $4$ then the product of its first $5$ terms is
If ${a^2} + a{b^2} + 16{c^2} = 2(3ab + 6bc + 4ac)$, where $a,b,c$ are non-zero numbers. Then $a,b,c$ are in