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 A007912 #21 Dec 17 2021 17:28:17
%S A007912 1,1,0,1,5,1,0,1,2,3,0,1,0,1,0,9,2,15,0,1,2,9,0,1,0,7,0,15,2,1,0,1,0,
%T A007912 27,0,1,0,25,0,21,2,11,0,1,45,33,0,25,0,39,0,27,0,49,0,1,57,15,0,1,0,
%U A007912 1,0,33,2,51,0,35,2,9,0,1,0,19,0,39,77,65,0,1,81,63,0,1,0,33,0,45,0
%N A007912 Quantum factorials: (n-1)!! - (n-2)!! (mod n).
%D A007912 S. P. Hurd and J. S. McCranie, Quantum factorials. Proceedings of the Twenty-fifth Southeastern International Conference on Combinatorics, Graph Theory and Computing (Boca Raton, FL, 1994). Congr. Numer. 104 (1994), 19-24.
%H A007912 T. D. Noe, <a href="/A007912/b007912.txt">Table of n, a(n) for n = 3..2000</a>
%H A007912 S. P. Hurd and J. S. McCranie, <a href="https://www.researchgate.net/publication/265637612_Quantum_factorials">Quantum factorials</a>, 1994.
%F A007912 a(n) = 0 iff n is odd and not a prime congruent to 3 modulo 4. - _Charlie Neder_, Feb 24 2019
%p A007912 a:= n-> (d-> irem(d(n-1)-d(n-2), n))(doublefactorial):
%p A007912 seq(a(n), n=3..100); # _Alois P. Heinz_, Dec 17 2021
%t A007912 Table[Mod[(n-1)!!-(n-2)!!,n],{n,3,100}] (* _Harvey P. Dale_, Aug 07 2012 *)
%Y A007912 Cf. A006882, A007911.
%K A007912 nonn,easy,nice
%O A007912 3,5
%A A007912 _J. H. Conway_