a(n) = Sum_{k=0..floor(n/2)} A026615(n, k).

Terms

a(0) =1a(1) =1a(2) =4a(3) =6a(4) =18a(5) =27a(6) =72a(7) =111a(8) =283a(9) =447a(10) =1112a(11) =1791a(12) =4381a(13) =7167a(14) =17305a(15) =28671a(16) =68497a(17) =114687a(18) =271560a(19) =458751a(20) =1077949a(21) =1835007a(22) =4283069a(23) =7340031a(24) =17031503a(25) =29360127a(26) =67768777a(27) =117440511a(28) =269797323a(29) =469762047