a(n) = Sum_{i=2^(n-1)..2^n-1} sigma_0(i), sigma_0(i) number of divisors of n, n positive integer.

Terms

a(0) =1a(1) =4a(2) =11a(3) =29a(4) =68a(5) =160a(6) =364a(7) =820a(8) =1813a(9) =3981a(10) =8674a(11) =18782a(12) =40387a(13) =86443a(14) =184232a(15) =391188a(16) =827787a(17) =1746443a(18) =3674573a(19) =7712561a(20) =16151933a(21) =33757505a(22) =70422235a(23) =146659055a(24) =304947023a(25) =633152157a(26) =1312820598a(27) =2718674046a(28) =5623413203a(29) =11618957217