A308638 a(n) is the number of k > 0 such that n-1-2*k > 0 and the points (n-1-2*k, a(n-1-2*k)), (n-1-k, a(n-1-k)) and (n-1, a(n-1)) are aligned.

0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 2, 3, 1, 1, 1, 1, 3, 0, 1, 2, 3, 1, 4, 2, 1, 3, 2, 4, 1, 1, 2, 2, 2, 3, 3, 4, 2, 3, 3, 2, 4, 4, 0, 1, 3, 2, 1, 3, 4, 5, 3, 6, 5, 3, 2, 6, 0, 3, 6, 4, 0, 3, 5, 5, 5, 4, 3, 6, 3, 3, 7, 3, 2, 3, 3, 2, 2, 1, 3, 5, 6, 4, 2, 4, 5

Offset

1,13

Comments

Is this sequence bounded?

Are there infinitely many null values?

Links

Rémy Sigrist, Table of n, a(n) for n = 1..10000

Rémy Sigrist, Scatterplot of the first 25000000 terms

Rémy Sigrist, C program for A308638

Example

The first terms, alongside the values of k such that (n-1-2*k, a(n-1-2*k)), (n-1-k, a(n-1-k)) and (n-1, a(n-1)), are:
  n   a(n)  k's
  --  ----  -----
   1     0  none
   2     0  none
   3     0  none
   4     1  1
   5     0  none
   6     1  2
   7     0  none
   8     1  2
   9     1  2
  10     0  none
  11     0  none
  12     1  4
  13     2  3,4
  14     3  1,4,5

Prog

(C) See Links section.

Crossrefs

See A308639 for a similar sequence.

Sequence in context: A122587 A276333 A347380 * A356320 A207572 A289623

Adjacent sequences: A308635 A308636 A308637 * A308639 A308640 A308641

Keyword

nonn,look

Author

Rémy Sigrist, Jun 13 2019

Status

approved