% Example to use prime numbers for page numbers

\version "2.13.51"

#(define (is-prime x k)
  (if (= x k) #t
   (if (= (remainder x k) 0) #f
    (is-prime x (+ k 1)))))

#(define (nth-prime n next)
  (if (= n 1) next
   (if (is-prime (+ 1 next) 2)
    (nth-prime (- n 1) (+ 1 next))
    (nth-prime n (+ 1 next)))))

%%%%

#(define-markup-command (page-number-compute layout props) ()
  (let ((page-number (chain-assoc-get 'page:page-number props 0)))
    (interpret-markup layout props (format "~a" (nth-prime page-number 2)))))

\header {
	title = "Mary Had a Little Lamb"
}

\paper {
	print-first-page-number = ##t
	oddHeaderMarkup = \markup {
	  \fill-line {
	    \larger \on-the-fly
	    	#print-page-number-check-first \page-number-compute
	    \null
	    \null
	  }
	}
	evenHeaderMarkup = \markup {
	  \fill-line {
	    \null
	    \null
	    \larger \on-the-fly
	    	#print-page-number-check-first \page-number-compute
	  }
	}
}

rh = \relative c' {
	e8 d c d e e e4 \pageBreak
	d8 d d4 e8 g g4  \pageBreak
	e8 d c d e e e e \pageBreak
	d d e d c2 \pageBreak
}

lh = \relative c {
	c8 <e g> g, <e' g> c <e g> g, <e' g>
	b <f' g> g, <f' g> c <e g> g, <e' g>
	c <e g> g, <e' g> c <e g> g, <e' g>
	b <f' g> g, <f' g> c <e g> c4
}

\score {
  \new PianoStaff <<
    \new Staff {
      \time 2/4 \key c \major \clef treble
      \rh \transpose c d \rh \key bes \major \transpose c bes \rh \bar "|."
    }
    \new Staff {
      \clef bass
      \lh \transpose c d \lh \key bes \major \transpose c bes \lh \bar "|."
    }
  >>
  \layout { }
}