设数列a1,a2,…,an,满足a1=a2=1,a3=2,且对任何自然数n,都有anan+1an+2≠1,又anan+1an+2an+3=an+an+1+an+2+an+3,则a1+a2+…+a100的值是_________________.
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设数列a1,a2,…,an,满足a1=a2=1,a3=2,且对任何自然数n,都有anan+1an+2≠1,又anan+1an+2an+3=an+an+1+an+2+an+3,则a1+a2+…+a100的值是_________________.
设数列a1,a2,…,an,满足a1=a2=1,a3=2,且对任何自然数n,都有anan+1an+2≠1,又anan+1an+2an+3=an+an+1+an+2+an+3,则a1+a2+…+a100的值是_________________.
设数列a1,a2,…,an,满足a1=a2=1,a3=2,且对任何自然数n,都有anan+1an+2≠1,又anan+1an+2an+3=an+an+1+an+2+an+3,则a1+a2+…+a100的值是_________________.
看不懂你出的题- - !
anan+1an+2是个什么式子
an*a(n+1)*a(n+2)*a(n+3)=an+a(n+1)+a(n+2)+a(n+3)
a(n+1)*a(n+2)*a(n+3)*a(n+4)=a(n+1)+a(n+2)+a(n+3)+a(n+4)
两式相减,整理有
(a(n+4)-an)(a(n+1)*a(n+2)*a(n+3)-1)=0
由a1=1,a2=1,a3=2,求出a4=4,a2*a3*a4=8...
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an*a(n+1)*a(n+2)*a(n+3)=an+a(n+1)+a(n+2)+a(n+3)
a(n+1)*a(n+2)*a(n+3)*a(n+4)=a(n+1)+a(n+2)+a(n+3)+a(n+4)
两式相减,整理有
(a(n+4)-an)(a(n+1)*a(n+2)*a(n+3)-1)=0
由a1=1,a2=1,a3=2,求出a4=4,a2*a3*a4=8不等于1,所以a(n+1)*a(n+2)*a(n+3)-1不恒等于0
所以
a(n+4)-an=0
所以数列是a1=1,a2=1,a3=2,a4=4的循环数列
循环数列 1,1,2,4,1,1,2,4...
S100=(1+1+2+4)*25=200
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