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 A131397 #13 Nov 29 2017 03:34:19 %S A131397 3,6,7,9,12,14,15,18,20,22,23,26,28,29,32,33,36,38,40,42,44,45,47,50, %T A131397 52,54,55,58,60,62,64,66,68,70,72,74,76,79,81,83,85,86,88,90,92,94,96, %U A131397 98,100,102,104,106,109,110,113,115,116,118,120,122,124,126,128,130,132 %N A131397 Positions of negative integers in A131394, minus 1. %C A131397 If A131394 is a permutation of the integers, as conjectured, then A131397 is the complement of A131396. %H A131397 <a href="/A131397/b131397.txt">Table of n, a(n) for n = 1..65</a> %F A131397 a(n) = position of n-th negative integer in A131394, minus 1. %e A131397 The 5th negative integer to occur in A131394 is -5, which occurs at position 13, so that a(5) = 13 - 1 = 12. %Y A131397 Cf. A131388, A131389, A131390, A131391, A131392, A131393, A131394, A131395, A131396. %K A131397 nonn %O A131397 1,1 %A A131397 _Clark Kimberling_, Jul 06 2007