Verifies that an item is a real number or an integer
(numberp item)
T if item evaluates to a real or an integer; otherwise nil.
Command: (setq a 123 b 'a)
A
Command: (numberp 4)
T
Command: (numberp 3.8348)
T
Command: (numberp "Howdy")
nil
Command: (numberp a)
T
Command: (numberp b)
nil
Command: (numberp (eval b))
T