2571141domain: NAppears in sequencesInvariant number of polygons of n-circum-C_5 H_5 systems.at n=14A122678Define a pair of sequences c_n, d_n by c_0=0, d_0=1 and thereafter c_n = c_{n-1}+d_{n-1}, d_n = c_{n-1}+4*n+2; sequence here is d_n.at n=27A192750