Number of 3's in n-th term of A007651.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =1a(7) =2a(8) =3a(9) =4a(10) =5a(11) =6a(12) =8a(13) =11a(14) =15a(15) =22a(16) =26a(17) =32a(18) =44a(19) =56a(20) =74a(21) =100a(22) =126a(23) =163a(24) =220a(25) =284a(26) =376a(27) =486a(28) =627a(29) =817