N=2005+2(1+2+3+...+2004)=2005+2*2004x2005/2=2005+2004x2005=2005(1+2004)=2005x2005=2005^2 deci patrat perfect
a=1^2004+2005^2006+2006^2005
1^2004 =1
2005^2006 ultima cifra 5
2006^2005 ultima cifra 6
1^2004+2005^2006+2006^2005 = se termina in 1+5+6= 12 deci in 2
Ultima cifra a unui patrat perfect poate fi 0, 1, 4, 5, 6, 9
rezulta ca a nu este patrat perfect deoarece se termina in 2