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 A106487 #11 Jul 23 2025 15:25:06 %S A106487 1,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,1,2, %T A106487 2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,2,3,3,4, %U A106487 3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,3,4,4,5,4,5 %N A106487 Number of leaves in combinatorial game trees. %C A106487 See the comment at A106486. %C A106487 After n=0 differs from A000120 for the first time at n=64, where A000120(64)=1, while a(64)=2. %e A106487 3 = 2^0 + 2^1 = 2^(2*0) + 2^((2*0)+1) encodes the CGT tree \/ which has two terminal nodes, thus a(3)=2. %e A106487 64 = 2^6 = 2^(2*3), i.e. it encodes the CGT tree %e A106487 \/ %e A106487 .\ %e A106487 which also has two terminal (non-root) nodes, so a(64)=2. %o A106487 (Scheme) (define (A106487 n) (cond ((zero? n) 1) (else (apply + (map A106487 (map shr (on-bit-indices n))))))) (define (shr n) (if (odd? n) (/ (- n 1) 2) (/ n 2))) (define (on-bit-indices n) (let loop ((n n) (i 0) (c (list))) (cond ((zero? n) (reverse! c)) ((odd? n) (loop (/ (- n 1) 2) (1+ i) (cons i c))) (else (loop (/ n 2) (1+ i) c))))) %Y A106487 Cf. A000120, A106486. %K A106487 nonn %O A106487 0,4 %A A106487 _Antti Karttunen_, May 21 2005