Maximum number of regions into which the plane can be divided using n (concave) quadrilaterals.

Terms

a(0) =1a(1) =2a(2) =18a(3) =50a(4) =98a(5) =162a(6) =242a(7) =338a(8) =450a(9) =578a(10) =722a(11) =882a(12) =1058a(13) =1250a(14) =1458a(15) =1682a(16) =1922a(17) =2178a(18) =2450a(19) =2738a(20) =3042a(21) =3362a(22) =3698a(23) =4050a(24) =4418a(25) =4802a(26) =5202a(27) =5618a(28) =6050a(29) =6498