getindex
getindex(x::Number)
getindex(c::Char)
f(n,m)=[n>i>1<j<m for i=1:n,j=1:m]
Julia, 29 bytes f(x)=x>1&&1+f(x%2>0?3x+1:x/2) I can't seem to compile Julia 0.1 on my machine, so there's a chance this is non-competing.
zip(t,t[2:end])