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 A296864 #11 Jan 22 2023 20:50:54 %S A296864 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,20,21,22,23,26,27,31,32,36,37, %T A296864 40,41,42,43,47,48,52,53,56,57,58,60,61,62,63,64,65,66,67,68,72,73,76, %U A296864 77,78,80,84,85,86,87,90,91,95,97,98,99,102,103,104,105 %N A296864 Numbers whose base-4 digits d(m), d(m-1), ..., d(0) have #(pits) = #(peaks); see Comments. %C A296864 A pit is an index i such that d(i-1) > d(i) < d(i+1); a peak is an index i such that d(i-1) < d(i) > d(i+1). The sequences A296864-A296866 partition the natural numbers. See the guides at A296882 and A296712. %H A296864 Clark Kimberling, <a href="/A296864/b296864.txt">Table of n, a(n) for n = 1..10000</a> %e A296864 The base-4 digits of 105 are 1, 2, 2, 1; here #(pits) = 0 and #(peaks) = 0, so 105 is in the sequence. %t A296864 z = 200; b = 4; %t A296864 d[n_] := Differences[Sign[Differences[IntegerDigits[n, b]]]]; %t A296864 Select[Range [z], Count[d[#], -2] == Count[d[#], 2] &] (* A296864 *) %t A296864 Select[Range [z], Count[d[#], -2] < Count[d[#], 2] &] (* A296865 *) %t A296864 Select[Range [z], Count[d[#], -2] > Count[d[#], 2] &] (* A296866 *) %Y A296864 Cf. A296882, A296712, A296865, A296866. %K A296864 nonn,base,easy %O A296864 1,2 %A A296864 _Clark Kimberling_, Jan 09 2018