Trinomial coefficients, Fibonacci numbers and units of the group <math altimg=''si1.svg''> <mi mathvariant=''script''>U</mi> <mo stretchy=''false''>(</mo> <mi mathvariant=''double-struck''>Z</mi> <msub> <mrow> <mi>C</mi> </mrow> <mrow> <mi>p</mi> </mrow> </msub> <</math>