<Dd> f (x) = ∑ n a n n! x n, (\ displaystyle f (x) = \ sum _ (n) (\ frac (a_ (n)) (n!)) x ^ (n),) </Dd> <P> we have the nth derivative at 0: </P> <Dl> <Dd> f (n) (0) = a n . (\ displaystyle f ^ ((n)) (0) = a_ (n).) </Dd> </Dl> <Dd> f (n) (0) = a n . (\ displaystyle f ^ ((n)) (0) = a_ (n).) </Dd>

What is the formula of f. a. s