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 A327139 #14 Jun 22 2021 01:06:56 %S A327139 1,4,7,10,13,16,19,23,26,29,32,35,38,41,45,48,51,54,57,60,63,67,70,73, %T A327139 76,79,82,85,89,92,95,98,101,104,107,111,114,117,120,123,126,129,133, %U A327139 136,139,142,145,148,151,155,158,161,164,167,170,173,176,180,183 %N A327139 Numbers k such that cos(2k) > cos(2k+2) < cos(2k+4). %C A327139 The sequences A327138, A327139, A327140 partition the positive integers. %H A327139 Clark Kimberling, <a href="/A327139/b327139.txt">Table of n, a(n) for n = 1..10000</a> %F A327139 (cos 2, cos 4, ...) = (-0.4, -0.6, 0.9, -0.1, -0.8, ...) approximately, so that the differences, in sign, are - + - - + - - + - - + +, with "+" in places 2,5,8,11,12,... (A327138), "- +" starting in places 1,4,7,10,13,... (A327139), and "- - +" starting in places 3,6,9,22,25,... (A327140). %t A327139 z = 500; f[x_] := f[x] = Cos[2 x]; t = Range[1, z]; %t A327139 Select[t, f[#] < f[# + 1] &] (* A327138 *) %t A327139 Select[t, f[#] > f[# + 1] < f[# + 2] &] (* A327139 *) %t A327139 Select[t, f[#] > f[# + 1] > f[# + 2] < f[# + 3] &] (* A327140 *) %Y A327139 Cf. A026309, A246303, A026317, A327138. %K A327139 nonn,easy %O A327139 1,2 %A A327139 _Clark Kimberling_, Aug 23 2019