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A294923 Number n such that the whole sequence of the first n terms of A293700 is a palindrome. 3
1, 3, 5, 7, 9, 11, 13, 15, 17, 46, 83, 120, 157, 194, 231, 268, 305, 342, 379, 416, 453, 490, 527, 564, 601, 638, 675, 712, 749, 786, 823, 860, 897, 934, 971, 1008, 1045, 1082, 1119, 1156, 9105, 19792, 51817, 83842, 201253, 318664, 436075, 553486 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A293700 are the first differences of A293698 which are the positive integers i such that floor(tan(i))=1.

A293701 are the lengths of the longest palindromic subsequences in the first n terms of A293700.

LINKS

Table of n, a(n) for n=1..48.

V.J. Pohjola, Line plot for n=1..50

EXAMPLE

The first 3 terms of A293701 are (3,19,3) which is a palindromic sequence, so 3 is a term.

The first 4 terms of A293701 are (3,19,3,19) which is not a palindromic sequence, so 4 is not a term.

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.

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.

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.

MATHEMATICA

rootsp7 = Flatten[Position[Table[Floor[Tan[n]], {n, 1, 10^7}], 1]];

difp7 = Differences[rootsp7];

nx = {}; Do[

If[Table[difp7[[i]], {i, 1, n}] == Reverse[Table[difp7[[i]], {i, 1, n}]],

  AppendTo[nx, n]], {n, 1, Length[difp7]}]

nx

CROSSREFS

Cf. A293701, A293700, A293698, A294924.

Sequence in context: A248608 A143450 A225563 * A005842 A204458 A192861

Adjacent sequences:  A294920 A294921 A294922 * A294924 A294925 A294926

KEYWORD

nonn

AUTHOR

V.J. Pohjola, Nov 11 2017

STATUS

approved

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Last modified March 18 12:10 EDT 2019. Contains 321283 sequences. (Running on oeis4.)