*** Bug 9352 has been marked as a duplicate of this bug. ***

Indeed, "annada" is probably not a recognized keyword for arithmetic expressions. :)

This template uses the page name of the *including* page in arithmetic
expressions via the {{PAGENAME}} variable. When used in context of a year page
(eg [[oc:2000]]) the page name is a number and thus works in the expression.

When viewing the raw template, of course, that doesn't do anything very useful

• but it doesn't have to.

While ugly, this isn't a bug. You could perhaps wrap the whole template in a
check for the page title or something to hide it, or use a <includeonly>, or
something, but that's a cosmetic issue of how you want it to display when viewed
"raw".