{an}是首项a1=1,公差d=3的等差数列,如果an=2011,则序号n等于?

{an}是首项a1=1,公差d=3的等差数列,如果an=2011,则序号n等于?
{an}是首项a1=1,公差d=3的等差数列,如果an=2011,则序号n等于?

{an}是首项a1=1,公差d=3的等差数列,如果an=2011,则序号n等于?
an=a1+(n-1)*d 式中,a1=1,d=3.an=2011.
1+(n-1)*3=2011.
3n-3+1=2011.
3n=2011+2
3n=2013.
n=671.
答；符合题设的项数（序号）n=671.