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 A129815 #11 Aug 24 2023 11:54:10 %S A129815 0,0,1,2,6,22,102,506,2952,18502,131112,991226,8271792,73176262, %T A129815 703077552,7121578106,77437418112,883521487942,10726837356672, %U A129815 136104948161786,1825110309733632 %N A129815 Number of reverse alternating fixed-point-free permutations on n letters. %C A129815 From _Emeric Deutsch_, Aug 06 2009: (Start) %C A129815 Reverse alternating permutations are called also up-down permutations. %C A129815 a(n) is also the number of reverse alternating permutations having exactly 1 fixed point (see the Stanley reference). Example: a(4)=2 because we have 1423 and 2314. %C A129815 (End) %H A129815 R. P. Stanley, <a href="https://arxiv.org/abs/math/0603520">Alternating permutations and symmetric functions</a>, arXiv:math/0603520 [math.CO], 2006. %F A129815 a(2n-1) = A129817(2n-1). [_Emeric Deutsch_, Aug 06 2009] %e A129815 a(4)=2 because we have 3412 and 2413. [_Emeric Deutsch_, Aug 06 2009] %Y A129815 Cf. A000111, A000166, A007779, A129817. %K A129815 more,nonn %O A129815 1,4 %A A129815 _Vladeta Jovovic_, May 20 2007 %E A129815 a(21) from _Alois P. Heinz_, Jun 11 2015