Find the sum 1+3+9+…+2187

Answer 1

To find the sum of this sequence, we need to calculate the sum of a geometric series.

The first term, $a$, is 1.
The common ratio, $r$, is 3.
The last term, $n$, is 2187.

The formula for the sum of a geometric series is:

$S = a \frac{r^n - 1}{r - 1}$

Substitute $a = 1$, $r = 3$, and $n = 2187$ into the formula:

$S = 1 \frac{3^{2187} - 1}{3 - 1}$
$S = 1 \frac{7625597484987 - 1}{2}$
$S = 1 \frac{7625597484986}{2}$
$S = 1 * 3812798742493$
$S = 3812798742493$

Therefore, the sum of the sequence 1+3+9+…+2187 is 3,812,798,742,493.