control radix in which number are printed
Major Section:  IO

By default, integers and ratios are printed in base 10. ACL2 also supports printing in radix 2, 8, or 16 by calling set-acl2-print-base with the desired radix (base).

  :set-acl2-print-base 10   ; Default printing
  (set-acl2-print-base 10)  ; Same as above
  :set-acl2-print-base 16   ; Print integers and ratios in hex, e.g., #x3A
  (set-acl2-print-base 16)  ; Same as above

Note: ACL2 events and some other top-level commands (for example, thm, verify, and history commands such as :pe and :pbt) set the print base to 10 during their evaluation. So set-acl2-print-base has no effect while these forms are being processed.