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

Author

Rémy Sigrist, Jun 13 2019

Keywords

• nonn
• look

Comments

Is this sequence bounded?

Are there infinitely many null values?

Examples

			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
		

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

Crossrefs

See A308639 for a similar sequence.

Programs

C

See Links section.