a(n) = round(Shi(n)) where Shi(x) is the sinh integral function.

Terms

a(0) =0a(1) =1a(2) =3a(3) =5a(4) =10a(5) =20a(6) =43a(7) =96a(8) =220a(9) =519a(10) =1246a(11) =3036a(12) =7480a(13) =18599a(14) =46596a(15) =117478a(16) =297780a(17) =758319a(18) =1938952a(19) =4975454a(20) =12807826a(21) =33063593a(22) =85572336a(23) =221983185a(24) =577057696a(25) =1502975453a(26) =3921470496a(27) =10248248560a(28) =26822559296a(29) =70299597879