Partial sums of A018190.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =34a(5) =115a(6) =446a(7) =1881a(8) =8386a(9) =38472a(10) =179701a(11) =849285a(12) =4047541a(13) =19415118a(14) =93623028a(15) =453486806a(16) =2205081449a(17) =10758731196a(18) =52651373968a(19) =258365785954