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 A127389 #7 Jul 09 2025 04:09:59
%S A127389 1,1,0,1,2,4,10,23,56,138,344,870,2220,5716,14828,38717,101682,268416,
%T A127389 711810,1895432,5066030,13586082,36547534,98593064,266661162,
%U A127389 722953814,1964358938,5348367006,14589803090,39870312218,109136843138
%N A127389 Number of fixed points in range [A014137(n-1)..A014138(n-1)] of permutations A127377/A127378 and A127387.
%F A127389 G.f. satisfies: A(x) = (1 + x*A(x)^2)*(1+x)/(1+x+2*x^2).
%o A127389 (PARI) {a(n)=local(A=1+x+x*O(x^n));for(i=0,n,A=(1 + x*A^2)*(1+x)/(1+x+2*x^2));polcoeff(A,n)}
%Y A127389 This is INVERTi transform of A086625 (appropriately shifted). I.e. INVERT([1, 1, 0, 1, 2, 4, 10, 23, 56, 138, 344, 870, 2220, 5716]) gives: 1, 2, 3, 6, 12, 26, 59, 138, 332, 814, 2028, 5118, ... (beginning of A086625)
%K A127389 nonn
%O A127389 0,5
%A A127389 _Antti Karttunen_, Jan 16 2007
%E A127389 Generating function, PARI-program and most of the terms supplied by _Paul D. Hanna_, Jan 15 2007