7360512domain: NAppears in sequencesa(0) = 0 by convention; for n>0, a(n) is the number of edges in the n-th figure shown in A255011 (meaning the figure with 4n points on the perimeter).at n=27A331448a(n) = Sum_{k=0..floor(n/3)} 2^k * 3^(n-3*k) * binomial(k,3*(n-3*k)).at n=40A392042