BaseForm
[expr, n]A binary integer:
BaseForm[33, 2]
A hexadecimal number:
BaseForm[234, 16]
A binary real number:
BaseForm[12.3, 2]
BaseForm[-42, 16]
BaseForm[x, 2]
BaseForm[12, 3] // FullForm
Bases must be between 2 and 36:
BaseForm[12, -3]
BaseForm[12, 100]