a(n) = Sum_{r=0..2^(n-1)} Binomial(2^n,2r)*3^r.A084594a(n) = Sum_{r=0..2^(n-1)} Binomial(2^n,2r)*3^r.Terms a(0) =1a(1) =4a(2) =28a(3) =1552a(4) =4817152External referencesoeis: A084594