Răspuns :
2 013 + 2 x ( 1 + 2 + 3 + .......+ 2012 ) =
= 2 013 + 2 x 2012 x ( 1 + 2012 ) / 2 =
= 2 013 + 2012 x 2013 =
= 2013 x ( 1 + 2012 ) =
= 2013 x 2013 =
= 2 013²→ patrat pefect
2 013 + 2 x ( 1 + 2 + 3 + .......+ 2012 ) =
= 2 013 + 2 x 2012 x ( 1 + 2012 ) / 2 =
= 2 013 + 2012 x 2013 =
= 2013 x ( 1 + 2012 ) =
= 2013 x 2013 =
= 2 013²→ patrat pefect