g=googolplex // 12 symbols
a[n]b-hyper operator // 20 symbols
f(x,y,z,t)=f(f(x-1,y,z,t),f(x-1,y,z,t),f(x-1,y,z,t),t-1) if x,y,z,t>2, ow: f=x[y]z // 82 symbols*
h(x)=f(h(x-1),h(x-1),h(x-1),h(x-1)) if x>0, ow: h=f(g,g,g,g) // 60 symbols*
h(g) // 4 symbols
The rest of the 500 symbols I'd use to explain why this is useless, but I'm not in the mood right now to give it a good scorn.
*I realize y=z everywhere in my use of f, so the same can be done with a 3-argument function and reduce the length, but let's leave it for clarity.