430416domain: NAppears in sequencesa(1)=7; a(n),a(n+1) are smallest > a(n-1) such that a(n-1)^2+a(n)^2=a(n+1)^2.at n=15A077035Number of n X 5 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 0 1 and 1 0 1 vertically.at n=20A207450a(n) = 3*a(n-2) - a(n-3) with a(0)=0, a(1)=3, a(2)=0.at n=21A214699