11477712896domain: NAppears in sequencesa(n) = 2*a(n-1) + 4*a(n-2), a(0)=1, a(1)=2.at n=20A063727Horadam sequence (0,1,4,2).at n=21A085449a(n) = Sum_{k=0..n} binomial(2n+1, 2k)*5^(n-k).at n=10A102592