aN=(2^N+1)^2-(2^N-1)^2=(2^N+1+2^N-1)(2^N+1-2^N+1)=2^(N+1)*2=2^(N+2)=2^(N-1)*2*4=2^(N-1)*8
∵N≥1且N为自然数,∴N-1≥0,∴aN=2^(N-1)*8是8的倍数
aN=(2^N+1)^2-(2^N-1)^2=(2^N+1+2^N-1)(2^N+1-2^N+1)=2^(N+1)*2=2^(N+2)=2^(N-1)*2*4=2^(N-1)*8
∵N≥1且N为自然数,∴N-1≥0,∴aN=2^(N-1)*8是8的倍数