There are (at least) two equations known as Sommerfeld's formula. The first is

where is a Bessel Function of the First Kind. The second states that under appropriate restrictions,

**References**

Iyanaga, S. and Kawada, Y. (Eds.). *Encyclopedic Dictionary of Mathematics.* Cambridge, MA: MIT Press,
pp. 1472 and 1474, 1980.

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1999-05-26