# Thread: n-th derivative of e^y and the partition function

1. ## n-th derivative of e^y and the partition function

Suppose $y=f(x)$ is $n$-times differentiable on some interval. For any partition $\alpha: a_1 + \cdots + a_k = n, \ a_j \geq 1,$ define $y^{\alpha}=\prod_{j=1}^k \frac{d^{a_j}y}{dx^{a_j}}.$

Example: for $n=5$ and the partitions $\alpha: 1 + 1 + 1 + 2 = 5$ and $\beta: 2+3=5$ we have $y^{\alpha}= (y')^3y''$ and $y^{\beta}=y''y'''.$

True or false: $\frac{d^n e^y}{dx^n}=\left(\sum_{\alpha} c_{\alpha}y^{\alpha} \right)e^y,$ where the sum is over all the partitions of $n$ and $c_{\alpha}$ are some positive integers depending on $n.$