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 A327845 #16 Oct 07 2019 09:15:04
%S A327845 1,2,4,12,40,132,428,1668,7628,36924,199000,1161824,7231332
%N A327845 Number of permutations of {1,2,...,n} such that for every k >= 1, the k-th differences are distinct.
%C A327845 a(n) <= A131529(n).
%e A327845 For n = 5 the a(5) = 40 solutions are one of following ten permutations, or a reversal, complement, or reversal and complement of one of these permutations:
%e A327845 [1,3,4,2,5]
%e A327845 [1,4,3,5,2]
%e A327845 [1,4,5,3,2]
%e A327845 [1,5,2,4,3]
%e A327845 [1,5,3,2,4]
%e A327845 [2,1,4,5,3]
%e A327845 [2,1,5,3,4]
%e A327845 [2,3,5,1,4]
%e A327845 [2,4,1,5,3]
%e A327845 [2,5,4,1,3]
%e A327845 As a non-example, [1,5,4,2,3] does not satisfy the k-th differences property, because while its first differences ([4,-1,-2,1]) and its second differences ([-5,-1,3]) are distinct, its third differences ([4,4]) are not.
%Y A327845 Cf. A130783, A131529, A327743.
%K A327845 nonn,more
%O A327845 1,2
%A A327845 _Peter Kagey_, Sep 27 2019
%E A327845 a(11) from _Giovanni Resta_, Sep 29 2019
%E A327845 a(12)-a(13) from _Freddy Barrera_, Oct 07 2019