Upper (1/5,1/2) midsequence of (2^n) and (5*n); see Comments.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =14a(5) =19a(6) =28a(7) =44a(8) =72a(9) =125a(10) =230a(11) =438a(12) =850a(13) =1671a(14) =3312a(15) =6592a(16) =13148a(17) =26257a(18) =52474a(19) =104906a(20) =209766a(21) =419483a(22) =838916a(23) =1677780a(24) =3355504a(25) =6710949a(26) =13421838a(27) =26843614a(28) =53687162a(29) =107374255