## Encyclopedia > Pi (letter)

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# Pi (letter)

Pi (Π π) is the 16th letter of the Greek alphabet and has a numeric value of 80.

The upper-case letter Π is used as a symbol for:

The lower-case letter π is used as a symbol for:

 Rotational inertia ... for that bunch of particles around that axis will be: $I = \sum_n r_n^2 m_n$ Continuous mass distributions require an infinite sum over all ...