Ulam spiral

[logoliv]

Hi all,

Damien's code doesn't work for me in HP Prime Pro app for iOS, nor in HP Prime Virtual Calculator for Windows... I have the last versions in both cases.

When I run the app I obtain the same error message :
"Error: Bad argument type" on "IF isprime(n) THEN"

What am I doing wrong ? Does isprime() function work in emulators programs ?
I'm new to HP Prime and it's my first program, thanks in advance for any help.

Olivier