Cogrowth sequence of the 20-element Frobenius group Frob20 = <S,T | S^5, T^4, (ST)^4>.

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =1a(5) =1a(6) =3a(7) =7a(8) =15a(9) =27a(10) =51a(11) =99a(12) =199a(13) =403a(14) =819a(15) =1651a(16) =3303a(17) =6579a(18) =13107a(19) =26163a(20) =52327a(21) =104755a(22) =209715a(23) =419635a(24) =839271a(25) =1678131a(26) =3355443a(27) =6710067a(28) =13420135a(29) =26841907