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 A185013 #43 Jun 19 2024 09:16:05
%S A185013 0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
%T A185013 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 A185013 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
%N A185013 Characteristic function of {3}.
%C A185013 Number of connected 2-regular (simple) graphs with girth exactly 3.
%H A185013 J. S. Kimberley, <a href="/wiki/User:Jason_Kimberley/C_k-reg_girth_eq_g_index">Index of sequences counting connected k-regular simple graphs with girth exactly g</a>
%H A185013 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (1).
%F A185013 a(n) = A179184(n) - A185114(n).
%F A185013 a(n) = [n = 3], where [ ] is the Iverson bracket. - _Wesley Ivan Hurt_, Dec 13 2013
%p A185013 A185013:=n->1-abs(signum(3-n)); seq(A185013(n), n=0..100); # _Wesley Ivan Hurt_, Dec 13 2013
%t A185013 Table[KroneckerDelta[n, 3], {n, 0, 100}] (* _Wesley Ivan Hurt_, Dec 13 2013 *)
%o A185013 (PARI) A185013(n)=n==3 \\ _M. F. Hasler_, Oct 30 2019
%o A185013 (Python)
%o A185013 def A185013(n): return int(n==3) # _Chai Wah Wu_, Feb 04 2022
%Y A185013 The Euler transformation of this sequence is A079978.
%Y A185013 Characteristic function of {g}: A000007 (g=0), A063524 (g=1), A185012 (g=2), this sequence (g=3), A185014 (g=4), A185015 (g=5), A185016 (g=6), A185017 (g=7).
%K A185013 nonn,easy
%O A185013 0,1
%A A185013 _Jason Kimberley_, Oct 11 2011