Factorial

//Iteration
f=(n,p=1)=>{ while(n) p*=n--; return p }
//Recursion
f=n=>!n||n*f(~-n)
//Memory
f=n=>[...Array(n)].reduce((s,e,i)=>-~i*s,1)


main(int i, char **o) <% return o?printf("%d",main(atoi(1[o]),0)):i?i*main(~-i,o):1; %>