S = 1+2+22 +23+24 +...+220 chia hết cho 127

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S = (1+2+22 +23+24 +25+26) +(27+...+213)+(214+...220)

= (1+2+22 +23+24 +25+26) +27(1 +...+26)+214(1+...26)

= (1+2+22 +23+24 +25+26)(1+27+214)

= 127. (1+27+214) chia hết cho 127


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S = (1+2+22 +23+24 +25+26) +(27+...+213)+(214+...220)

= (1+2+22 +23+24 +25+26) +27(1 +...+26)+214(1+...26)

= (1+2+22 +23+24 +25+26)(1+27+214)

= 127. (1+27+214) chia hết cho 127



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