The functional relationship between y and n(n stands for the nth graph) is y = N2+5n+6;
(2) In terms of meaning, n2+5n+6=506, and n=20.
∴n=20；
(3) The number of white tiles is n (n+1) = 20 (20+1) = 420, and the number of black tiles is 506-420=86.
* * * needs 86×4+420×3= 1604 (yuan),
* * * Need to spend 1604 yuan to buy tiles;
(4)n(n+ 1)= N2+5n+6-n(n+ 1)。
The solution is n=
three
33
2
Because n is not an integer.
The number of black and white tiles varies.