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 A185014 #21 Jun 19 2024 09:15:23 %S A185014 0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %T A185014 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %U A185014 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A185014 Characteristic function of four. %C A185014 Number of connected 2-regular (simple) graphs with girth exactly 4. %C A185014 The Euler transformation of this sequence is A121262. %H A185014 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (1). %F A185014 a(n) = A185114(n) - A185115(n). %o A185014 (Python) %o A185014 def A185014(n): return int(n==4) # _Chai Wah Wu_, Feb 04 2022 %Y A185014 Characteristic function of g: A000007 (g=0), A063524 (g=1), A185012 (g=2), A185013 (g=3), this sequence (g=4), A185015 (g=5), A185016 (g=6), A185017 (g=7). %K A185014 nonn,easy %O A185014 0,1 %A A185014 _Jason Kimberley_, Sep 30 2011