The number of twin binary Niven numbers (k, k+1) such that k <= 2^n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =5a(7) =8a(8) =18a(9) =35a(10) =61a(11) =98a(12) =187a(13) =304a(14) =492a(15) =880a(16) =1583a(17) =2779a(18) =5196a(19) =9407a(20) =17387a(21) =31772a(22) =58450a(23) =106360a(24) =193875a(25) =351836a(26) =642844a(27) =1173333a(28) =2155913a(29) =3993379