A178976 Number of collinear triples in graph of preceding terms.

0, 0, 0, 1, 1, 1, 2, 4, 4, 4, 5, 5, 5, 6, 8, 11, 11, 12, 12, 12, 14, 14, 14, 16, 18, 20, 22, 24, 26, 29, 29, 29, 30, 31, 32, 35, 35, 35, 37, 38, 40, 43, 43, 45, 46, 50, 51, 52, 55, 55, 57, 57, 59, 61, 63, 65, 69, 69, 74, 74, 74, 76, 77, 78, 81, 82, 82, 86, 89, 91, 93, 96, 99, 100, 104, 105, 106, 107, 108, 112, 113, 115, 115, 117, 121, 122, 122, 124, 124, 125, 126, 131, 133, 134, 137, 139, 141, 146, 148, 150

Offset: 0

Author

Alex Abercrombie, Jan 06 2011

Keywords

• nonn
• easy

Comments

a(n) is the number of 3-element subsets (i0 and a(k)-a(j)=a(j)-a(i).

The sequence appears to grow faster than n but slower than n^(1+c) for any positive c.

Examples

			For n=7, the triples (0,1,2),(0,3,6),(2,4,6),(3,4,5) satisfy the stated conditions, so a(7)=4