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 A218618 #13 Jul 25 2025 16:46:46
%S A218618 0,1,-1,1,-1,3,1,-1,3,5,-1,1,-1,3,5,-1,-7,1,1,3,1,-1,3,5,-1,-7,1,1,3,
%T A218618 -7,1,1,-5,1,-5,-3,-1,1,-1,3,5,-1,-7,1,1,3,-7,1,1,-5,1,-5,-3,-1,-7,1,
%U A218618 1,-5,1,11,1,1,13,1,-5,-1,3,1,-1,3,5,-1,-7,1,1,3
%N A218618 Absolute value of a(n) tells the size of the n-th side-tree ("tendril", A213730(n)) in the binary beanstalk; the sign tells on which side of the infinite trunk (A179016) it is.
%C A218618 Positive and negative terms correspond to the tendrils that sprout respectively at the left and right sides of the infinite trunk, when the beanstalk is drawn with the lesser numbers branching to the left. The absolute values give the sizes of those tendrils, with all nodes included: The leaves, the internal vertices as well as the root itself: A213730(n).
%H A218618 Antti Karttunen, <a href="/A218618/b218618.txt">Table of n, a(n) for n = 0..8727</a>
%F A218618 a(n) = -1^A213730(n) * A213727(A213730(n)).
%o A218618 (Scheme) (define (A218618 n) (* (expt -1 (A213730 n)) (A213727 (A213730 n))))
%Y A218618 Partial sums: A218785, A218789. Cf. also A218786, A218613.
%K A218618 sign
%O A218618 0,6
%A A218618 _Antti Karttunen_, Dec 03 2012