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 A296891 #7 Jan 21 2023 17:59:38 %S A296891 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26, %T A296891 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49, %U A296891 50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67 %N A296891 Numbers whose base-13 digits d(m), d(m-1), ..., d(0) have #(pits) = #(peaks); see Comments. %C A296891 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 A296891-A296894 partition the natural numbers. See the guides at A296712 and A296882. %H A296891 Clark Kimberling, <a href="/A296891/b296891.txt">Table of n, a(n) for n = 1..10000</a> %e A296891 The base-13 digits of 2550 are 1,2,1,2; here #(pits) = 1 and #(peaks) = 1, so 2550 is in the sequence. %t A296891 z = 200; b = 13; %t A296891 d[n_] := Differences[Sign[Differences[IntegerDigits[n, b]]]]; %t A296891 Select[Range [z], Count[d[#], -2] == Count[d[#], 2] &] (* A296891 *) %t A296891 Select[Range [z], Count[d[#], -2] < Count[d[#], 2] &] (* A296892 *) %t A296891 Select[Range [z], Count[d[#], -2] > Count[d[#], 2] &] (* A296893 *) %Y A296891 Cf. A296882, A296712, A296892, A296893. %K A296891 nonn,base,easy %O A296891 1,2 %A A296891 _Clark Kimberling_, Jan 10 2018