It is also the number of primordial nuclides without energetically allowed baryon number-preserving decay modes.
90 is the third unitary perfect number.
In Greek-based number-naming systems, 90 is associated with prefix "enneaconta-", and with prefix "nonaginti-" in Latin systems.
As a banknote denomination
The third Burmese kyat had banknotes with this number in the denomination.
For this reason, it has been used in a song by the Sportfreunde Stiller.
- OEIS, Sequence A002808 (accessed 2021-02-07)