The calculator I always wanted

[Valentin Albillo]

(09-16-2019 08:33 PM)vanLudwig Wrote:  I wondered for which integers n is the sum of the first n primes itself prime? 2 is prime. 2+3=5 is prime. 2+3+5=10 is not. 2+3+5+7=17 is prime. 2+3+5+7+11=28 is not. Turns out, it happens a lot.
$$\texttt{Select}\left ( \left \{ n \right \}_{n=1}^{2500}, n \mapsto \sum_{i=1}^{n} p_{i}\in \mathbb{P} \right )$$

Very nice. You can make it run faster by noticing that, apart from the initial "1", n must necessarily be even.

V.