3-(-1)=7-3=11-7=4数列是以-1为首项,4为公差的等差数列,设此数列为{an}.an=-1+4(n-1)=4n-5a100=4×100-5=395令4n-5=2009n=(2009+5)/4=2014/4=503.5,不是整数,而项数应为正整数,因此2009不是数列的项.令4n-5=2011n=(2...