(+ 2 fill-column)
72

(concat "you" " have" " 2 " "candies.")
"you have 2 candies."

(concat "The " (+ 2 fill-column) " red foxes.")
Debugger entered--Lisp error: (wrong-type-argument sequencep 72)
  concat("The " 72 " red foxes.")
  eval((concat "The " (+ 2 fill-column) " red foxes."))
  eval-last-sexp-1(t)
  eval-last-sexp(t)
  eval-print-last-sexp()
  call-interactively(eval-print-last-sexp nil nil)

(concat "The " (int-to-string (+ 2 fill-column)) " red foxes.")
(concat "The " (number-to-string (+ 2 fill-column)) " red foxes.")
"The 72 red foxes."