A276204 a(0) = a(1) = 0. For n>1 a(n) is the smallest nonnegative integer such that there is no arithmetic progression k,m,n (of length 3) such that a(k)+a(m) = a(n).

0, 0, 1, 0, 0, 1, 2, 2, 1, 0, 0, 1, 0, 0, 1, 2, 2, 1, 4, 4, 1, 4, 4, 1, 2, 2, 1, 0, 0, 1, 0, 0, 1, 2, 2, 1, 0, 0, 1, 0, 0, 1, 2, 2, 1, 4, 4, 1, 4, 4, 1, 2, 2, 1, 7, 7, 1, 7, 7, 1, 2, 2, 1, 7, 7, 1, 7, 7, 1, 2, 2, 1, 4, 4, 1, 4, 4, 1, 2, 2, 1, 0, 0, 1, 0, 0, 1, 2, 2, 1, 0, 0, 1, 0, 0, 1, 2, 2, 1, 4, 4, 1, 4, 4, 1, 2, 2, 1, 0, 0, 1, 0, 0, 1, 2, 2, 1, 0, 0, 1, 0

Offset

0,7

Comments

The sequence has the same set of values as A033627.

The sequence has a kind of a "triple rhythm", compare the distribution of zeros to the Cantor set.

Conjecture 1:

One can calculate a(n) in a following, non-recursive way, using the ternary representation of n.

Let n>=0 be an integer. We consider two cases:

1. There is no digit 2 in the ternary representation of n. Then a(n) = 0.

2. There is a digit 2 in the ternary representation of n.

Let i be the number of the position (counting from right) of the rightmost digit 2 in ternary representation of n, then a(n) = A033627(i).

For example: let n = 19. The ternary representation of 19 is 201. The rightmost digit 2 in the number 201 is on the third position (counting from right), so a(19) = A033627(3) = 4.

Conjecture 2:

The sequence can be generated in a following way:

Start with a zero. Take three consecutive copies of all you have, replace all zeros in the third copy with the next value of A033627, repeat.

Both of these conjectures can be generalized for similarly defined sequences where the length of the arithmetic progression in the definition (in A276204 it is 3) is a prime number, see A276206.

The assumption about primality is essential, for complex lengths of the arithmetic progression the sequence is irregular, see A276205.

Links

Michal Urbanski, Table of n, a(n) for n = 0..199999

Example

For n = 6 we have that:
a(6)>0, because a(0)+a(3)=0 and 0,3,6 is an arithmetic progression.
a(6)>1, because a(4)+a(5)=0 and 4,5,6 is an arithmetic progression.
There is no such arithmetic progression k,m,6 that a(k)+a(m) = 2, so a(6) = 2.

Crossrefs

Cf. A276205 (length 4), A276206 (length 5), A276207 (any length).

Cf. A033627, A229037.

Sequence in context: A210502 A350797 A283988 * A365573 A370278 A369245

Adjacent sequences: A276201 A276202 A276203 * A276205 A276206 A276207

Keyword

nonn,hear

Author

Michal Urbanski, Aug 24 2016

Status

approved