508677193728domain: NAppears in sequencesa(n+1) = 4*(a(n)+a(n-1)) for n>1, a(1)=1, a(2)=6.at n=18A108051Expansion of (1 + 6*x - 12*x^2 - 8*x^3)/(1 - 24*x^2 + 16*x^4).at n=17A164584