When the summation is equal to factorial and primorial products?

56 Views Asked by At

Is it known when the summation is equal to factorial ?

$$ n! = \sum_{i=1}^{m}i = \frac{m(m+1)}{2} $$

where $n,m \in \mathbb{N}$

$$ 3! = \sum_{i=1}^{3}i = 6 $$

$$ 5! = \sum_{i=1}^{15}i = 120 $$

And also when product of primes is equal to summation:

$$ \prod_{i=1}^{n}P_i = \sum_{i=1}^{m}i $$

where $P_n$ is the $n$th prime and $m \in \mathbb{N}$

$$ \prod_{i=1}^{2}P_i = 2\times3 = \sum_{i=1}^{2}i = 6 $$

$$ \prod_{i=1}^{4}P_i = 2\times3\times5\times7 = \sum_{i=1}^{20}i = 210 $$

I was not able to find other pairs of factorial and primorial which are equals to summation.

I would like to know how to prove that other pairs either exist or doesn't exist.