This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A126303 #5 Mar 31 2012 13:21:13 %S A126303 0,1,2,1,3,2,2,1,2,4,3,3,2,3,3,2,2,1,2,3,2,3,2,5,4,4,3,4,4,3,3,2,3,4, %T A126303 3,4,3,4,3,3,2,3,3,2,2,1,2,3,2,3,2,4,3,3,2,3,4,3,4,3,3,2,3,2,3,6,5,5, %U A126303 4,5,5,4,4,3,4,5,4,5,4,5,4,4,3,4,4,3,3,2,3,4,3,4,3,5,4,4,3,4,5,4,5,4 %N A126303 a(n) = number of nodes with odd distance to the root in the n-th plane general tree encoded by A014486(n). Both internal and terminal nodes (leaves) are counted. %e A126303 A014486(27) = 696 (1010111000 in binary), encodes the following general plane tree, where the root is marked with * and nodes with even or odd distance to root with 'e's and 'o's, respectively. %e A126303 .......o %e A126303 .......| %e A126303 .......e %e A126303 .......| %e A126303 ...o.o.o %e A126303 ....\|/. %e A126303 .....*.. %e A126303 there are four nodes marked with 'o', thus a(27)=4. %o A126303 (MIT Scheme:) (define (A126303 n) (*A126303 (A014486->parenthesization (A014486 n)))) %o A126303 (define (*A126303 s) (cond ((null? s) 0) (else (fold-left (lambda (x y) (+ x 1 (*A126304 y))) 0 s)))) %Y A126303 a(n) = A072643(n)-A126305(n). Cf. A126304. Scheme-function A014486->parenthesization given in A014486. %K A126303 nonn %O A126303 0,3 %A A126303 _Antti Karttunen_, Jan 02 2007