The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A368189 Number of (undirected) cycles in the n-Pell graph. 1
 0, 1, 65, 4983940 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Table of n, a(n) for n=1..4. Eric Weisstein's World of Mathematics, Graph Cycle. Eric Weisstein's World of Mathematics, Pell Graph. PROG (Python) from itertools import product, combinations, groupby, islice from networkx import empty_graph, simple_cycles def A368189(n): if n<=1 : return 0 G = empty_graph(v for v in product((0, 1, 2), repeat=n) if not any(len(list(g))&1 and k==2 for k, g in groupby(v))) for a, b in combinations(G, 2): r = tuple(islice((i for i in range(n) if a[i]!=b[i]), 3)) if len(r)==1 and a[r[0]]!=2 and b[r[0]]!=2: G.add_edge(a, b) elif len(r)==2 and r[0]+1==r[1] and a[r[0]] and b[r[0]] and a[r[0]]==a[r[1]] and b[r[0]]==b[r[1]]: G.add_edge(a, b) return sum(1 for c in simple_cycles(G)) # Chai Wah Wu, Jan 18 2024 CROSSREFS Sequence in context: A238612 A185823 A035519 * A238842 A059755 A215657 Adjacent sequences: A368186 A368187 A368188 * A368190 A368191 A368192 KEYWORD nonn,more AUTHOR Eric W. Weisstein, Dec 16 2023 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 17 18:23 EDT 2024. Contains 374377 sequences. (Running on oeis4.)