From Engel product expansion of 4/7.

Terms

a(0) =3a(1) =3a(2) =4a(3) =4a(4) =6a(5) =17a(6) =36a(7) =44a(8) =49a(9) =74a(10) =122a(11) =126a(12) =744a(13) =7814a(14) =9238a(15) =9432a(16) =52114a(17) =33241100a(18) =85747623a(19) =353210861a(20) =355051655a(21) =1950030118a(22) =32235431345a(23) =50590143817a(24) =58937626393a(25) =482819610949