9999999999²
= (10000000000 - 1)²
= 10000000000² - 2*10000000000 + 1
= 10000000000 0000000000 - 20000000000 + 1
= (9999999999 0000000000 + 10000000000)- 20000000000 + 1
= (9999999998 0000000000 + 20000000000)- 20000000000 + 1
= 9999999998 0000000000 + 1
= 99999999980000000001
或按照规律
9*9 = 81
99*99 = 9801
999*999 = 998001
推得9999999999的平方 = 9个9,1个8,9个0,1个1
因此共有9+1 = 10个奇数数字