Split PDF every nth page and convert output to PDF/A

spezzaPDFA.sh

#!/bin/bash 
COUNTER=1
NUMBEROFPAGES=<LAST_PAGENUMBER_IN_INPUT_PDF>
while [  $COUNTER -lt $NUMBEROFPAGES ]; do
 pdftk input.pdf cat $COUNTER-$((COUNTER+1)) output OUTPUT${COUNTER}.pdf
  gs -dPDFA -dBATCH -dNOPAUSE -sProcessColorModel=DeviceCMYK -sDEVICE=pdfwrite -sPDFACompatibilityPolicy=1 -sOutputFile=OUTPUT${COUNTER}_A.pdf OUTPUT${COUNTER}.pdf
  let COUNTER=COUNTER+2 
done