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%I #6 Nov 19 2018 19:37:08
%S 0,2,4,6,8,10,13,15,17,19,21,23,25,27,29,31,34,36,38,40,42,44,46,48,
%T 50,52,54,57,59,61,63,65,67,69,71,73,75,78,80,82,84,86,88,90,92,94,96,
%U 98,101,103,105,107,109,111,113,115,117,119,122,124,126,128
%N Nonnegative integers k satisfying sec(k) < sec(k+1) > sec(k+2).
%C A246407, A246408, and A246409 partition the nonnegative integers.
%H Clark Kimberling, <a href="/A246408/b246408.txt">Table of n, a(n) for n = 1..1000</a>
%t z = 500; f[x_] := f[x] = Sec[x];
%t Select[Range[0, z], f[#] > f[# + 1] &] (* A246407 *)
%t Select[Range[0, z], f[#] < f[# + 1] > f[# + 2] &] (* A246408 *)
%t Select[Range[0, z], f[#] < f[# + 1] < f[# + 2] > f[# + 3] &] (* A246409 *)
%t Join[{0},Position[Partition[Sec[Range[130]],3,1],_?(#[[1]] <#[[2]]> #[[3]]&), 1,Heads->False]//Flatten] (* _Harvey P. Dale_, Nov 19 2018 *)
%Y Cf. A246407, A246409.
%K nonn,easy
%O 1,2
%A _Clark Kimberling_, Aug 25 2014
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