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 A185015 #23 Jun 19 2024 09:15:01 %S A185015 0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %T A185015 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 A185015 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A185015 Characteristic function of 5. %C A185015 Number of connected 2-regular (simple) graphs with girth exactly 5. %C A185015 The Euler transformation of this sequence is A079998. %H A185015 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (1). %F A185015 a(n) = A185115(n) - A185116(n). %o A185015 (Python) %o A185015 def A185015(n): return int(n==5) # _Chai Wah Wu_, Feb 04 2022 %Y A185015 Characteristic function of g: A000007 (g=0), A063524 (g=1), A185012 (g=2), A185013 (g=3), A185014 (g=4), this sequence (g=5), A185016 (g=6), A185017 (g=7). %K A185015 nonn,easy %O A185015 0,1 %A A185015 _Jason Kimberley_, Sep 30 2011