Răspunsuri

2014-06-25T17:38:35+03:00
1+5+5²+5³+5⁴+...+5²⁰¹³=
=(1+5)+5²(1+5)+5⁴(1+5)+....+5²⁰¹²(1+5)=
=(1+5)(1+5²+5⁴+...+5²⁰¹²)=
=6* (1+5²+5⁴+...+5²⁰¹²)
=> este divizibil cu 6