cp's OEIS Frontend

A294923 Number n such that the whole sequence of the first n terms of A293700 is a palindrome.

%I A294923 #18 Feb 26 2018 12:15:28
%S A294923 1,3,5,7,9,11,13,15,17,46,83,120,157,194,231,268,305,342,379,416,453,
%T A294923 490,527,564,601,638,675,712,749,786,823,860,897,934,971,1008,1045,
%U A294923 1082,1119,1156,9105,19792,51817,83842,201253,318664,436075,553486
%N A294923 Number n such that the whole sequence of the first n terms of A293700 is a palindrome.
%C A294923 A293700 are the first differences of A293698 which are the positive integers i such that floor(tan(i))=1.
%C A294923 A293701 are the lengths of the longest palindromic subsequences in the first n terms of A293700.
%H A294923 V.J. Pohjola, <a href="https://palindromesdotblog.files.wordpress.com/2018/02/lognx-1-50-a294923.pdf">Line plot for n=1..50</a>
%e A294923 The first 3 terms of A293701 are (3,19,3) which is a palindromic sequence, so 3 is a term.
%e A294923 The first 4 terms of A293701 are (3,19,3,19) which is not a palindromic sequence, so 4 is not a term.
%e A294923 The first 17 terms of A293701 are (3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3) which is a palindromic sequence, so 17 is a term.
%e A294923 The first 18 terms of A293701 are (3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 3) which is not a palindromic sequence, so 18 is not a term.
%e A294923 The first 19 terms of A293701 are (3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 19, 3, 3, 16) which is not a palindromic sequence, so 19 is not a term.
%t A294923 rootsp7 = Flatten[Position[Table[Floor[Tan[n]], {n, 1, 10^7}], 1]];
%t A294923 difp7 = Differences[rootsp7];
%t A294923 nx = {}; Do[
%t A294923 If[Table[difp7[[i]], {i, 1, n}] == Reverse[Table[difp7[[i]], {i, 1, n}]],
%t A294923   AppendTo[nx, n]], {n, 1, Length[difp7]}]
%t A294923 nx
%Y A294923 Cf. A293701, A293700, A293698, A294924.
%K A294923 nonn
%O A294923 1,2
%A A294923 _V.J. Pohjola_, Nov 11 2017