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Characteristic function of 7.
15

%I #20 Jun 18 2024 12:00:28

%S 0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

%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 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

%N Characteristic function of 7.

%C Number of connected 2-regular (simple) graphs with girth exactly 7.

%C The Euler transformation of this sequence is A082784.

%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (1).

%F a(n) = A185117(n) - A185118(n).

%o (Python)

%o def A185017(n): return int(n==7) # _Chai Wah Wu_, Feb 04 2022

%Y Characteristic function of g: A000007 (g=0), A063524 (g=1), A185012 (g=2), A185013 (g=3), A185014 (g=4), A185015 (g=5), A185016 (g=6), this sequence (g=7).

%Y Cf. A185117, A185118.

%K nonn,easy

%O 0,1

%A _Jason Kimberley_, Oct 14 2011