68132domain: NAppears in sequencesNumber of compositions of n with equal number of even and odd parts.at n=21A098123a(1) = 1; a(n+1) = Sum_{d|n} sigma(n/d)*a(d), where sigma = sum of divisors (A000203).at n=47A307817Number of convex polygons on the lines of a triangular grid with edge length n.at n=14A340130