restart:
 
 # g(n) calcutates the number-theoretic function considered by Collatz
 
 n := 6: # Change to whatever you wish
 
 interface(screenwidth=72);
 
 g := proc(n:posint)
 local m;
 m := modp(n,3);
 if m = 0 then 2*n/3;
 elif m=1 then (4*n-1)/3;
 else (4*n+1)/3;
 fi;
 end:
 
 
 print(`g(` .n. `)` = g(n));

                                   g(6) = 4