#!/bin/bash

exec find /store/planet/notes/20?? -maxdepth 1 -type f -iname 'planet-notes-??????.osn*' -printf '%T@ %p\n' | \
  sort -k 1nr | \
  sed 's/^[^ ]* //' | \
  tail -n +17 | \
  xargs -r rm -f