cent: 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 Debian possible default full paths are:

/usr/lib/x86_64-linux-gnu/gap/pkg/guava/bin/leon/cent - from package: gap-guava-bin

You may install the required package with command apt-get install {package}

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