LUT with Size 500 000

A LUT with 500,000 entries? And how many bits is each entry?

I suggest you declare an array and then use the inital block to set the values.

reg [7:0] lut_rom [0:499_999];

integer i;

initial begin

for(i = 0; i < 500_000; i = i+1) begin

lut_rom[i] = ....

end

end

Reads should be performed in such a way that Quartus can infer a synchronous ROM from this. Otherwise, it will probably not fit and/or be very slow.