Number of 2's in n-th term of A006711.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =1a(5) =1a(6) =2a(7) =4a(8) =8a(9) =6a(10) =10a(11) =9a(12) =14a(13) =16a(14) =21a(15) =28a(16) =38a(17) =45a(18) =69a(19) =86a(20) =123a(21) =157a(22) =210a(23) =280a(24) =363a(25) =480a(26) =622a(27) =818a(28) =1104a(29) =1453