% http://b-p-i.blogspot.ro/2013/03/numbering-first-line-lineno-modulo.html
\usepackage[modulo]{lineno}
\let\oldLineNumber=\LineNumber%
\def\LineNumber{%
    \ifnum \value{linenumber}=1%
            \strut\thelinenumber%
        \else%
            \oldLineNumber%
    \fi%
    }