✔ 最佳答案
(1) 2010 = 2 × 3 × 5 × 67
除了1以外,因數為2, 3, 5, 67, 2×3, 2×5, 2×67,3×5,3×67,5×67,2×3×5,
2×3×67, 2×5×67, 3×5×67及2×3×5×67
即1,2,3,5,6,10,15,30,67,134,201,335,402,670,1005及2010
(2)n=8m+3其中m為整數
7^n (mod 10)
≡7^(8m + 3) (mod 10)
≡7^3 × (7^4 )^2m (mod 10)
≡343 × (2401)^2m (mod 10)
≡3 × 1 (mod 10)
≡3 (mod 10)
所以7^n 的個位數字是3
(3)n=2010000…0002010
=2010 × 10^2006 + 2010
n^2 = (2010 × 10^2006 + 2010)^2
=2010^2 × (10^2006 + 1)^2
=4040100× (10^4012 + 2×10^2006 + 1)
=4040100 × 10^4012 + 8080200 × 10^2006 + 4040100
所有數字之和 = 9 + 18 + 9 = 36
(4) 10^2009 + 1 (mod 7)
≡(7 + 3)^2009 + 1 (mod 7)
≡3^2009 + 1 (mod 7)
≡[3^(7 - 1)]^334 × 3^5+1 (mod 7)
≡(1)^334 × 3^5+1 (mod 7) Since 3^(7 - 1) ≡ 1 (mod 7) by Fermat little theorem
≡3^5 + 1 (mod 7)
≡244 (mod 7)
≡6 (mod 7)
餘數是6
(5)n和2010除了1以外不能有共同因數.
除1以外和2010沒共同因數的有2010 × (1 - 1/2) × (1 - 1/3) × (1 - 1/5) × (1 - 1/67)
=528個