Great idea, that was fun!
Rot 13:
Bar glcb: N2 (pbyhza1ebj2) fubhyq or hafunqrq va yiy7 gb nyybj lbh gb tb sebz yiy8. Vg’f pheeragyl vzcbffvoyr naq gur fbyhgvba cqs vf nyfb jebat (vg fubjf lbh ragrevat yriry 7 ng N3)
Gur ‘yriryf ba gur fnzr cntr ner pbaarpgrq’ uvag va gur fbyhgvba thvqr vf gehr ohg abg arprffnel, fvapr yriryf ba frcnengr cntrf ner nyfb pbaarpgrq. (Sbe rknzcyr, tbvat onpx naq sbegu orgjrra 7 naq 6 ba qvssrerag cntrf.
Gur ahzorevat pnhfrq fbzr pbashfvba. Vg’f abg vaghvgvir gung tebhaq yriry naq yriry 0 ner sne ncneg engure guna orvat gur fnzr ‘urvtug’. Creuncf zber gurzngvp vs lbh pbhagrq onpxjneqf gb gur tebhaq yriry gb flzobyvmr tbvat qrrcre, fb vafgrnq bs gur cqs tbvat sebz yiy 1,2,3… vg jbhyq or erahzorerq gb tb sebz yiy-22,-21,-20… Gur gernfher ebbz jbhyq or yriry -23. Vg jbhyq gura or zber pyrne gung tebhaq yriry (juvpu lbh pbhyq nyfb ahzore 0) naq gur gernfher ebbz (-23) ner sne ncneg.
V guvax vg jbhyq’ir orra pbby vs gur gernfher cntr jnf gur irel svefg cntr va gur cqs, be uvqqra fbzrubj ba gur gvgyr cntr. Evtug abj, lbh qvt nyy gur jnl gb gur ‘gbc’ bs gur cqs naq fbzrubj tb gb gur ynfg cntr sebz gurer.