S = 17 + 172 + 173 + ... + 1718
S = 17 (1+17+172) + 174 (1+17+172) + .......+1716 (1+17+172)
S = 17. 307 + 174.307 +.............+ 1716.307
S = 307 (17+ 174+…………….+ 1716)
Vì 307 \(⋮\) 307 nên 307( 17+ 174+…………….+ 1716) \(⋮\) 307
Vậy S \(⋮\) 307