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Counting words (Posted on 2022-04-27) Difficulty: 3 of 5
Given an alphabet of 3 letters i.e. a,b,c evaluate
the number of n-letter words containing even number of “a”s.

No Solution Yet Submitted by Ady TZIDON    
Rating: 5.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: How to get to a closed form? | Comment 6 of 7 |
(In reply to How to get to a closed form? by Larry)

What I would do to find a closed form, assuming I don't want to go through the analytic process, would be to enter the first few numbers in the sequence. 


Putting 

2,5,14,41,122,365

into the OEIS leads to A007051 as the first of four sequences, except I wasn't including zero a's, so I had

1,6,25,90,301,966

which leads to A000392, Stirling numbers of the second kind.

  Posted by Charlie on 2022-04-27 13:39:00
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