a(n) = A000217(A000217(n)+1).

Terms

a(0) =1a(1) =3a(2) =10a(3) =28a(4) =66a(5) =136a(6) =253a(7) =435a(8) =703a(9) =1081a(10) =1596a(11) =2278a(12) =3160a(13) =4278a(14) =5671a(15) =7381a(16) =9453a(17) =11935a(18) =14878a(19) =18336a(20) =22366a(21) =27028a(22) =32385a(23) =38503a(24) =45451a(25) =53301a(26) =62128a(27) =72010a(28) =83028a(29) =95266