Calculate: $3+9+27+81+243+729+2187$.

Given: $3+9+27+81+243+729+2187$.

To do: To find the sum.

As given, $3+9+27+81+243+729+2187$

It can be written as: $3^1+3^2+3^3+ .... + 3^7$

The given question is in G.P.

As known

$a_1=3$ [First term in the sequence]

$r=3$   [The common ratio]

$n=7$   [Number of terms]

On using these values in the Sum equation $S=a_1( \frac{( 1-r_n)}{( 1-r)}) =3( \frac{1-3^7}{1-3})$

$=3( \frac{1-2187}{1-3})$

$=3( \frac{-2186}{-2})$

$=3\times1093$

$=3279$

Thus, $3+9+27+81+243+729+2187=3279$.