Răspuns :
(5+9+13+101):4=
5=2k+1
9=2p+1
13=2q+1
101=2l+1
=>[2(k+p+q+l)+4]÷4= rest 0
5+9+13+.....+101
Le descompunem.
(4x1+1)+(4x2+1)+(4x3+1)+.....+(4x25+1)
Dam 4 factor comun
4x(1+2+3+.....+25)
Daca am dat ,,4" factor comun se imparte exact la ,,4"
Sper ca te-am ajutat! :)