Giải thích các bước giải:
`S=(3+3^2+3^3+3^4)+(3^5+3^6+3^7+3^8)+...+(3^97+3^98+3^99+3^100)`
`S=120+(3^4 .3+3^4 .3^2+3^4 . 3^3+3^4 . 3^4)+...+(3^96 .3+3^96 .3^2+3^96 . 3^3+3^96 . 3^4)`
`S=120+3^4.(3+3^2 + 3^3+ 3^4)+...+3^96.(3+3^2+3^3+3^4)`
`S=120.1+3^4 . 120+...+3^96 . 120`
`S=120.(1+3^4+...+3^96)`
Vì `120\vdots40`
`=>S\vdots40`