9999*5556+6666*6666
=9999*(5555+1)+36*1111^2
=9999*5555+9999+36*1111^2
=45*1111^2+9999+36*1111^2
=(45+36)*1111^2+9999
=81*1111^2+9*1111
=(9*1111)^2+9*1111
=9*1111*(9999+1)
=9999*10000
=99990000.