题目: 数列{an}满足a1=1,an+1=2an+1,若数列{an+c}恰为等比数列,则c的值为______. 答案: ∵a1=1,an+1=2an+1,∴1+an+1=2(an+1)∴数列{an+1}是以2为公比的等比数列故答案为:1