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arata ca 2+2^2+2^3+....+2^2016 este divizibil cu 30

Răspuns :

2+2^2+2^3+....+2^2016 =
2016 :4=504   deci putem grupa cate 4
=
(2+2^2+2^3+2^4)+....+(2^13+2^14+2^15+2^2016) =
=(2+4+8+16)+....+2^12(2+2^2+2^3+2^4)=
=30+....+2^12×(2+4+8+16)=
=30+....+
2^12×30=
=30
×(1+...+2^12)  deci divizibil cu 30
2+2^2+2^3+....+2^2016 =
2016 :4=504   
(2+2^2+2^3+2^4)+....+(2^13+2^14+2^15+2^2016) =
=(2+4+8+16)+....+2^12(2+2^2+2^3+2^4)=
=30+....+2^12×(2+4+8+16)=
=30+....+
2^12×30=
=30
×(1+...+2^12)