isympy: 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/isympy - from package: sympy

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

On Debian possible default full paths are:

/usr/bin/isympy - from package: python-sympy

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

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