blackjack: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/blackjack - from package: gnome-games-extra

You may install the required package with command yum install {package}

Error in other languages:
blackjack: bevel nie gevind nie
blackjack: comandă negăsită
blackjack: comando não encontrado
blackjack: commande introuvable
blackjack: command not found
blackjack: käsku ei ole
blackjack: không tìm thấy lệnh
blackjack: komanda nerasta
blackjack: Kommando nicht gefunden.
blackjack: kommandot finns inte
blackjack: komut yok
blackjack: nie znaleziono polecenia
blackjack: níor aimsíodh an t-ordú
blackjack: no se encontró la orden
blackjack: no s'ha trobat l'ordre
blackjack: opdracht niet gevonden
blackjack: parancs nem található
blackjack: perintah tidak ditemukan
blackjack: príkaz nenájdený
blackjack: příkaz nenalezen
blackjack: команда не найдена
blackjack: командата не е открита
blackjack: 命令找不到
blackjack: コマンドが見つかりません