Given a number n and a pattern that follows like:

(1 to 26): a,b,c,….z

(27 to 52): aa,ab,ac,…az

(52 to 78): ba,bb,bc,…bz

. . . za,zb,zc,…zz

aaa,aab,aac,…aaz

aba,abb,abc,… . . . find the nth pattern