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valoarea nr:n este:
n=1+2+3-4+5+6+7-8+.....+61+62+63-64


Răspuns :

1+2+3+4+...+64-2(4+8+12+...+64)=
=64*65/2 - 8(1+2+..+16)=
=64*65/2 - 8*16*17/2=
=32*65-64*17=
=2080-1088=992