54651domain: NAppears in sequencesNumber of bipartite partitions.at n=21A002767Numbers k such that k divides A109227(k); or k such that A109227(k) is a Niven number.at n=7A109228Rounded down ratio of area of a unit circle and one of the circles inscribed between a regular n-gon and a circumscribed unit circle.at n=21A244094