number?

user=> (number? 1)
true
user=> (number? 1.0)
true
user=> (number? :a)
false
user=> (number? nil)
false
user=> (number? "23")
false

;; map number? over the vector
(map number? [1 0.44 3e6 0xFF])
;;=> (true true true true)

;; map number? over the vector created by converting a list into a vector 
;; with the function "into"
(map number? (into [] '(1 0.44 3e6 0xFF)))
;;=> (true true true true)

;; Works for rationals
user=> (number? (/ 2 3))
true

;; Warning! NaN is considered as a number in member of the class Double.
;; this may be confusing, but it's good to know,
;; especially if you are working with filters
user=> (number? Double/NaN)
true
user=> (filter number? [nil 0 1.1 "String" {:key :val} Double/NaN])
(0 1.1 ##NaN)