15690529806domain: NAppears in sequencesNumber of vertices in Sierpiński triangle of order n.at n=21A067771a(0) = 2, a(n) = 3*a(n-1) - 3.at n=22A115098a(n) = 6 * A015518(n).at n=21A120471a(n) = 3*A132357(n).at n=20A135264