A185014 Characteristic function of four.

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, 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, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset: 0

Author

Jason Kimberley, Sep 30 2011

Keywords

• nonn
• easy

Comments

Number of connected 2-regular (simple) graphs with girth exactly 4.

The Euler transformation of this sequence is A121262.

Links

• Index entries for linear recurrences with constant coefficients, signature (1).

Crossrefs

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).

Programs

Python

def A185014(n): return int(n==4) # Chai Wah Wu, Feb 04 2022

Formula

a(n) = A185114(n) - A185115(n).