gp-2.7: 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/bin/gp-2.7 - from package: pari-gp

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

Error in other languages:
gp-2.7: bevel nie gevind nie
gp-2.7: comandă negăsită
gp-2.7: comando não encontrado
gp-2.7: commande introuvable
gp-2.7: command not found
gp-2.7: käsku ei ole
gp-2.7: không tìm thấy lệnh
gp-2.7: komanda nerasta
gp-2.7: Kommando nicht gefunden.
gp-2.7: kommandot finns inte
gp-2.7: komut yok
gp-2.7: nie znaleziono polecenia
gp-2.7: níor aimsíodh an t-ordú
gp-2.7: no se encontró la orden
gp-2.7: no s'ha trobat l'ordre
gp-2.7: opdracht niet gevonden
gp-2.7: parancs nem található
gp-2.7: perintah tidak ditemukan
gp-2.7: príkaz nenájdený
gp-2.7: příkaz nenalezen
gp-2.7: команда не найдена
gp-2.7: командата не е открита
gp-2.7: 命令找不到
gp-2.7: コマンドが見つかりません