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 A130686 #16 Dec 14 2023 05:24:48
%S A130686 1,2,3,6,5,4,7,2,1,0,1,2,7,4,5,6,3,2,1,0,1,2,3,6,5,4,7,2,1,0,1,2,7,4,
%T A130686 5,6,3,2,1,0,1,2,3,6,5,4,7,2,1,0,1,2,7,4,5,6,3,2,1,0,1,2,3,6,5,4,7,2,
%U A130686 1,0,1,2,7,4,5,6,3,2,1,0,1,2,3,6,5,4,7,2,1,0,1,2,7,4,5,6,3,2,1,0,1,2,3,6,5
%N A130686 Absolute difference of final digits of two consecutive triangular numbers.
%C A130686 Periodic with period 20.
%H A130686 <a href="/index/Rec#order_20">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1).
%F A130686 a(n) = abs{ A010879[A000217(n+1)] - A010879[A000217(n)] }. - _R. J. Mathar_, Jul 15 2007
%p A130686 A000217 := proc(n) n*(n+1)/2 ; end: A010879 := proc(n) n mod 10 ; end: A130686 := proc(n) abs(A010879(A000217(n+1))-A010879(A000217(n))) ; end: seq(A130686(n),n=0..80) ; # _R. J. Mathar_, Jul 15 2007
%Y A130686 Cf. A008954.
%K A130686 base,easy,nonn
%O A130686 1,2
%A A130686 _Giovanni Teofilatto_, Jun 30 2007