Number of integers with a shortest addition chain of length n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =9a(6) =15a(7) =26a(8) =44a(9) =78a(10) =136a(11) =246a(12) =432a(13) =772a(14) =1382a(15) =2481a(16) =4490a(17) =8170a(18) =14866a(19) =27128a(20) =49544a(21) =90371a(22) =165432a(23) =303475a(24) =558275a(25) =1028508a(26) =1896704a(27) =3501029a(28) =6465774a(29) =11947258