This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A178976 #12 Jul 22 2025 08:17:03 %S A178976 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, %T A178976 26,29,29,29,30,31,32,35,35,35,37,38,40,43,43,45,46,50,51,52,55,55,57, %U A178976 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 %N A178976 Number of collinear triples in graph of preceding terms. %C A178976 a(n) is the number of 3-element subsets (i<j<k) of (0,...,n-1) such that both i,j,k and a(i),a(j),a(k) are arithmetic progressions (including the case a(i)=a(j)=a(k)). That is, k-j=j-i>0 and a(k)-a(j)=a(j)-a(i). %C A178976 The sequence appears to grow faster than n but slower than n^(1+c) for any positive c. %e A178976 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 %K A178976 nonn,easy %O A178976 0,7 %A A178976 _Alex Abercrombie_, Jan 06 2011