- 61 is an odd prime number.
- 61 is the 9th Mersenne exponent.
- 61 is equivalent to gagthree using the Gag- prefix.
- Greek-based number-naming systems, 61 is associated with prefix "henhexaconta-", and with prefix "unsexaginti-" in Latin systems.
- It is one of the values of the weak Goodstein function: \(g(5)=61\).
- It is equal to gag-three with the gag prefix, since A(3,3) in the Ackermann function equals 61.
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