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 A296879 #7 Jan 21 2023 18:05:07 %S A296879 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 A296879 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49, %U A296879 50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67 %N A296879 Numbers whose base-9 digits d(m), d(m-1), ..., d(0) have #(pits) = #(peaks); see Comments. %C A296879 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 A296879-A296881 partition the natural numbers. See the guides at A296882 and A296712. %H A296879 Clark Kimberling, <a href="/A296879/b296879.txt">Table of n, a(n) for n = 1..10000</a> %e A296879 The base-9 digits of 67 are 7,4; here #(pits) = 0 and #(peaks) = 0, so 67 is in the sequence. %t A296879 z = 200; b = 9; %t A296879 d[n_] := Differences[Sign[Differences[IntegerDigits[n, b]]]]; %t A296879 Select[Range [z], Count[d[#], -2] == Count[d[#], 2] &] (* A296879 *) %t A296879 Select[Range [z], Count[d[#], -2] < Count[d[#], 2] &] (* A296880 *) %t A296879 Select[Range [z], Count[d[#], -2] > Count[d[#], 2] &] (* A296881 *) %Y A296879 Cf. A296882, A296712, A296880, A296881. %K A296879 nonn,base,easy %O A296879 1,2 %A A296879 _Clark Kimberling_, Jan 09 2018