Perimeter (rounded down) of Pi-shaped box fractal after n iterations.

Terms

a(0) =1a(1) =2a(2) =5a(3) =15a(4) =39a(5) =103a(6) =269a(7) =700a(8) =1821a(9) =4736a(10) =12313a(11) =32016a(12) =83242a(13) =216429a(14) =562716a(15) =1463063a(16) =3803966a(17) =9890311a(18) =25714810a(19) =66858508a(20) =173832121a(21) =451963515a(22) =1175105140a(23) =3055273364a(24) =7943710747a(25) =20653647942a(26) =53699484649