Associated Mersenne numbers.

Terms

a(0) =0a(1) =1a(2) =1a(3) =4a(4) =5a(5) =11a(6) =16a(7) =29a(8) =45a(9) =76a(10) =121a(11) =199a(12) =320a(13) =521a(14) =841a(15) =1364a(16) =2205a(17) =3571a(18) =5776a(19) =9349a(20) =15125a(21) =24476a(22) =39601a(23) =64079a(24) =103680a(25) =167761a(26) =271441a(27) =439204a(28) =710645a(29) =1149851