91/Historical Note

Historical Note on $91$ (Ninety-One)

There are $91$ days in a quarter-year: $13$ weeks of $7$ days each.

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $91$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $91$