Invariant number of internal vertices of n-circum-C_5 H_5 systems.

Terms

a(0) =0a(1) =5a(2) =25a(3) =80a(4) =225a(5) =605a(6) =1600a(7) =4205a(8) =11025a(9) =28880a(10) =75625a(11) =198005a(12) =518400a(13) =1357205a(14) =3553225a(15) =9302480a(16) =24354225a(17) =63760205a(18) =166926400a(19) =437019005a(20) =1144130625a(21) =2995372880a(22) =7841988025a(23) =20530591205a(24) =53749785600a(25) =140718765605a(26) =368406511225a(27) =964500768080