Given an alphabet of 3 letters i.e. a,b,c evaluate
the number of nletter words containing even number
of “a”s.
The closed form I found is: f(n) = (3^n + 1)/2
I found it by trial and error.
Is there a mathematical way to go from:
Sigma{even k <=n} C(n,k)*2^(nk)
to the closed form?

Posted by Larry
on 20220427 09:52:13 