a(n) = a(n-1) + 2^A047240(n) for n>1, a(1)=1.

Terms

a(0) =1a(1) =3a(2) =7a(3) =71a(4) =199a(5) =455a(6) =4551a(7) =12743a(8) =29127a(9) =291271a(10) =815559a(11) =1864135a(12) =18641351a(13) =52195783a(14) =119304647a(15) =1193046471a(16) =3340530119a(17) =7635497415a(18) =76354974151a(19) =213793927623a(20) =488671834567