diff --git a/captcha/experimental.sh b/captcha/experimental.sh
index d87f15d..ec794f5 100755
--- a/captcha/experimental.sh
+++ b/captcha/experimental.sh
@@ -150,7 +150,8 @@ INSTRUCTIONS2="...en remplaçant chaque X par la somme"
 # ****************************************************************************
 
 MODULES=(CALCUL NOTIN REPLACE REVERSE)
-RMODULE=`seq 0 $(( (#MODULES[@]) - 1)) | sort -R | head -n 1`
+NMODULES=#MODULES[@]
+RMODULE=`seq 0 $((NMODULES-1)) | sort -R | head -n 1`
 #eval "${MODULES[RMODULE]}"
 
 TEXT="$NEWINPUT"