can anyone give me the formula of the series... 1,1,5,17,61,217...

Ask iit jee aieee pet cbse icse state board community

Discussion Response Post to: can anyone give me the formula of the series... 1,1,5,17,61,217...

Forum Index -> Algebra -> View Full Question

Author

Message

Bipin Dubey (13679)

Forum Expert

total posts: 7942
Offline

analytical expression for n^th term can be found by generating polynomial which I learned from Hari sir.

We have to find : such that

Adding these three :

except 1st terms all terms are 0 since they follow a_n+2 = 3a_n+1 + 2a_n

we know a₁ = 1 and a₂ = 1. Expand RHS and compare coefficients of xⁿ to find out the analytical expression for a_n ( feeling a bit lazy so didn't do till last step :D )

however I can't figure out what will be the sum of the series

Bipin Kumar Dubey Chemical Dept. IIT Kharagpur

Like 0 people liked this

Free Sign Up!

Preparing for IIT-JEE ?

Arihant Revision Package for IIT JEE - Books, Practice Tests + Rank Predictor

@ INR 1,995/-

For Quick Info