restart: n := 7: # Change to whatever you wish
 # h(n) calculates the inverse of g, the number-theoretic 
 # function considered by Collatz
 
 h := proc(n:posint)
 local m;
 m := modp(n,4);
 if m = 1 then (3*n+1)/4;
 elif m=3 then (3*n-1)/4;
 else 3*n/2;
 fi;
 end:
 
 print(`h(` .n. `)` = h(n));