Engel expansion of the Madelung constant A085469.

Terms

a(0) =1a(1) =2a(2) =3a(3) =3a(4) =3a(5) =3a(6) =10a(7) =19a(8) =27a(9) =32a(10) =41a(11) =209a(12) =351a(13) =809a(14) =1235a(15) =3337a(16) =4109a(17) =43834