9^2=81
99^2=9801
999^2=998001
9999^2=99980001
99999^2=9999800001
.
99...9^2(n个9)=99.98000.01(n-1个9,n-1个0)
9999999999^2=99999999980000000001,有9个9,1 个1,共有10个奇数数学.