V
vulinhhuong2000
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a, (2+1)+(2^2+1)+(2^4+1)+(2^8+1)+(2^16+1)=2^32-1
b, (3+1)+(3^2+1)+(3^4+1)+(3^8+1)+(3^16+1)+(3^32+1)=1/2*(3^64-1)
b, (3+1)+(3^2+1)+(3^4+1)+(3^8+1)+(3^16+1)+(3^32+1)=1/2*(3^64-1)