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 A287796 #7 Jul 23 2025 15:42:02
%S A287796 0,1,2,3,4,5,6,7,8,9,10,9,8,7,6,5,4,3,2,1,2,3,4,5,6,7,8,9,10,11,10,9,
%T A287796 8,7,6,5,4,3,2,3,4,5,6,7,8,9,10,11,12,11,10,9,8,7,6,5,4,3,4,5,6,7,8,9,
%U A287796 10,11,12,13,12,11,10,9,8,7,6,5,4,5,6,7,8
%N A287796 Ten steps forward, nine steps back.
%H A287796 <a href="/index/Rec#order_20">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1).
%F A287796 a(n) = Sum_{i=1..n} (-1)^floor((2*i-2)/19).
%F A287796 a(n) = a(n-1) + a(n-19) - a(n-20) for n > 19.
%p A287796 A287796:=n->add((-1)^floor((2*i-2)/19), i=1..n): seq(A287796(n), n=0..200);
%t A287796 Table[Sum[(-1)^Floor[(2 i - 2)/19], {i, n}], {n, 0, 100}]
%Y A287796 Cf. A008611 (one step back, two steps forward).
%Y A287796 Cf. A058207 (three steps forward, two steps back).
%Y A287796 Cf. A260644 (four steps forward, three steps back).
%Y A287796 Cf. A271800 (five steps forward, four steps back).
%Y A287796 Cf. A271859 (six steps forward, five steps back).
%Y A287796 Cf. A287655 (seven steps forward, six steps back).
%Y A287796 Cf. A287793 (eight steps forward, seven steps back).
%Y A287796 Cf. A287794 (nine steps forward, eight steps back).
%K A287796 nonn,easy
%O A287796 0,3
%A A287796 _Wesley Ivan Hurt_, May 31 2017