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 A187804 #11 Jul 22 2025 10:55:10 %S A187804 1,0,3,0,19,0,0,0 %N A187804 Number of circular permutations of length n whose n flattenings are all not derangements. %C A187804 Circular permutations are permutations whose indices are from the ring of integers modulo n. For a circular permutation pi, a flattening at position k<n gives a straight permutation which preserves the relative order of pi. For example, the circular permutation (0,2,1) has the flattenings 021, 210, and 102. Note these three flattenings are all not derangements, so a(3) counts (0,2,1). %e A187804 For n=5 the a(5)=3 solutions are (0,3,1,4,2), (0,4,3,2,1), and (0,2,4,1,3). %K A187804 nonn,more %O A187804 3,3 %A A187804 _Isaac Lambert_, Jan 06 2013