a(n) = A277715(n) / 3.

Terms

a(0) =3a(1) =7a(2) =15a(3) =31a(4) =63a(5) =127a(6) =219a(7) =255a(8) =291a(9) =439a(10) =511a(11) =583a(12) =819a(13) =879a(14) =1023a(15) =1167a(16) =1443a(17) =1639a(18) =1747a(19) =1759a(20) =1915a(21) =2047a(22) =2115a(23) =2335a(24) =2887a(25) =3187a(26) =3279a(27) =3339a(28) =3495a(29) =3519