Say there is a list `[1,2,3,4,5]`

, I would need to get the count of all possible combinations of the elements (or ‘sub-lists’), e.g. `1, 2, 3, 4, 5, 12, 13, 14, ..., 123, 124, ..., 12345`

.

I know how to get `nCr`

, the count of combinations of `r`

elements of a list with total `n`

elements.

Python 3.8 or above:

```
from math import comb
p, r = 5, 2
print(comb(p, r))
```

Then I could do `nC1 + nC2 +...+ nCn`

. But is there a better/faster way?

```
p, result = 5, 0
for r in range(1, 6):
result += comb(p, r)
print(result)
```

Would appreciate your answers.

### >Solution :

This specific sum is equal to `2^n -1`

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