∴a2n+2=2×2 n-1,∴a2n=2 n-2.
又a2n+a2n+1= a2n+
a1+( a2+ a3)+ ( a4+ a5)+ ( a6+ a7)+ …+ ( a2006+ a2007)
= a1+(
= 1+(3×2-5)+ (3×22-5)+ (3×23-5)+ …+ (3×21003-5)
= 1+(3×2-5)+ (3×22-5)+ (3×23-5)+ …+ (3×21003-5)
= 3×(2+22+23+…+21003+1-5×1003
=6×(21003-1)+1-5×1003=6×21003- 5020 ,故选D.
- 答案