Number of regions in an equal-armed cross with arms of length n (see Comments for definition).

Terms

a(0) =4a(1) =104a(2) =568a(3) =1900a(4) =4808a(5) =10180a(6) =19180a(7) =33132a(8) =53628a(9) =82432a(10) =121448a(11) =172948a(12) =239356a(13) =323168a(14) =427272a(15) =554892a(16) =709476a(17) =893772a(18) =1111588a(19) =1367292a(20) =1664604a(21) =2008240a(22) =2402560a(23) =2852532a(24) =3363280a(25) =3938712a(26) =4585568a(27) =5308720a(28) =6112736a(29) =7006068