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A272727 a(0)=0; thereafter a(n+1) is the number of coincidences between  the sequence so far (a(0), ..., a(n)) and its reverse (a(n), ..., a(0)). 4
0, 1, 0, 3, 0, 3, 0, 5, 0, 7, 0, 7, 0, 7, 0, 9, 0, 9, 0, 11, 0, 13, 0, 15, 0, 15, 0, 15, 0, 15, 0, 17, 0, 19, 0, 19, 0, 19, 0, 21, 0, 21, 0, 23, 0, 23, 0, 25, 0, 27, 0, 29, 0, 31, 0, 31, 0, 31, 0, 31, 0, 31, 0, 33, 0, 33, 0, 35, 0, 37, 0, 39, 0, 39, 0, 39, 0, 39, 0, 41, 0, 43 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

a(2n-1) is positive and odd.

a(2n+1) - a(2n-1) is always either 0 or 2.

The number of repetitions of the value 2n-1 is A272729(n).

LINKS

Ivan Neretin, Table of n, a(n) for n = 0..8191

FORMULA

a(2n)=0.

a(2n-1)=A272728(n)+n.

EXAMPLE

A one-element series [0] coincides with its own reverse, hence a(1)=1.

[0,1] and [1,0] differ in every term, hence a(2)=0.

[0,1,0] is its own reverse, hence a(3)=3.

[0,1,0,3] and [3,0,1,0] differ in every term, hence a(4)=0.

[0,1,0,3,0] and [0,3,0,1,0] coincide in three terms, hence a(5)=3.

MATHEMATICA

Nest[Append[#, Count[# - Reverse[#], x_ /; x == 0]] &, {0}, 81]

CROSSREFS

Cf. A272728, A272729.

Sequence in context: A292130 A291971 A240923 * A100258 A045763 A132748

Adjacent sequences:  A272724 A272725 A272726 * A272728 A272729 A272730

KEYWORD

nonn

AUTHOR

Ivan Neretin, May 05 2016

STATUS

approved

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Last modified February 20 00:51 EST 2018. Contains 299357 sequences. (Running on oeis4.)