Number of 3's in n-th term of A006711.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =1a(6) =2a(7) =2a(8) =1a(9) =2a(10) =3a(11) =5a(12) =6a(13) =8a(14) =13a(15) =16a(16) =21a(17) =30a(18) =38a(19) =50a(20) =63a(21) =86a(22) =115a(23) =145a(24) =193a(25) =258a(26) =355a(27) =466a(28) =609a(29) =820