Fatal error: Call to undefined function is_even()

That’s because the is_even function isn’t defined. You can either make sure it’s defined in the themes function or replace it:

To replace it, you can use

$style = ( $blog_count % 2 ) ? 'even' : 'odd';

or define the is_even funtion

function is_even( $blog_count ) {
    if ( $blog_count % 2 )
        return true;
    return false;
}