Editing Birthday problem (section)

===Approximation of number of people===
This can also be approximated using the following formula for the ''number'' of people necessary to have at least a {{sfrac|1|2}} chance of matching:
:<math>n \geq \tfrac{1}{2} + \sqrt{\tfrac{1}{4} + 2 \times \ln(2) \times 365} = 22.999943.</math>
This is a result of the good approximation that an event with {{math|{{sfrac|1|''k''}}}} probability will have a {{sfrac|1|2}} chance of occurring at least once if it is repeated {{math|''k'' [[natural logarithm of 2|ln 2]]}} times.<ref>{{cite journal
 | last = Mathis
 | first = Frank H.
 |date= June 1991
 | title = A Generalized Birthday Problem
 | journal = SIAM Review
 | volume = 33
 | issue = 2
 | pages = 265–270
 | issn = 0036-1445
 | doi = 10.1137/1033051
 | oclc = 37699182
 | jstor = 2031144
 | url = http://http.cs.berkeley.edu/~daw/papers/genbday-crypto02.ps
 }}</ref>