<P> The infinite series whose terms are the natural numbers 1 + 2 + 3 + 4 + ⋯ is a divergent series . The nth partial sum of the series is the triangular number </P> <Dl> <Dd> ∑ k = 1 n k = n (n + 1) 2, (\ displaystyle \ sum _ (k = 1) ^ (n) k = (\ frac (n (n + 1)) (2)),) </Dd> </Dl> <Dd> ∑ k = 1 n k = n (n + 1) 2, (\ displaystyle \ sum _ (k = 1) ^ (n) k = (\ frac (n (n + 1)) (2)),) </Dd>

Who invented the formula n n+1 2