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