Similar questions have been asked before regarding journals that publish:
- expository work,
- recreational mathematics,
- computational results,
- new proofs of old theorems,
- and even math textbooxs.
However, I did not find any references to journals that publish new mathematical identities. These might include new formulae for $\pi$, $e$, or other known constants that might be useful for researchers in a wide variety of fields.
After briefly looking through papers that contain expositions of new formulae, it would seem that the majority of these papers are given "as-is", i.e., as notes freely available on the webpage of the author. Are there no journals that publish such results?
Best Answer
As Peter Heinig commented, if the mathematics behind the identity is novel and important enough, then you should select a journal like you would select a journal for any other paper—if it's a combinatorial identity, look for a combinatorics journal; if it's a number-theoretic identity, look for a number theory journal, etc.
For the specific case of constants such as $\pi$ and $e$, most novel identities for them are nowadays discovered with significant computer assistance. The journal Experimental Mathematics is one place where such identities have been published, e.g., I'm fond of Jesús Guillera's paper About a New Type of Ramanujan-Type Series, which contains some amazing identities such as the following one due to Gourevitch (which I believe is still open as of this writing):
$$\sum_{n=0}^\infty \frac{1+14n+76n^2+168n^3}{2^{20n}}\binom{2n}{n}^7 = \frac{32}{\pi^3}.$$