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Staff size maximising expected birthday holiday hours

Question

A company closes for the whole day on any date that is the birthday of at least one of its employees; on every other date all employees work 2424 hours. Birthdays are independent and uniform over 365365 days. The company wants to choose its head count nn to maximise the expected total number of employee-hours not worked in a year. What nn should it pick? Answer −1-1 if no finite nn is optimal.

Short answer

−1-1 (no finite optimum). The expected number of closed days is 365(1−(364/365)n)365\left(1-(364/365)^n\right), which increases with nn. Total hours off are 24n24n times that, a product of two increasing positive factors, so it grows without bound and more staff is always better.

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