cp's OEIS Frontend

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.

User: Ken McCabe

Ken McCabe's wiki page.

Ken McCabe has authored 1 sequences.

A365273 Number of vertices in the Laakso graph of order n.

Original entry on oeis.org

6, 30, 174, 1038, 6222, 37326, 223950, 1343694, 8062158, 48372942, 290237646, 1741425870, 10448555214, 62691331278, 376147987662, 2256887925966, 13541327555790, 81247965334734, 487487792008398, 2924926752050382
Offset: 1

Author

Ken McCabe, Aug 30 2023

Keywords

Comments

This can be proved using the definition of the Laakso graph. The Laakso graph of level 0 is two vertices joined by an edge. The level 1 Laakso graph L_1 is obtained by replacing part of the edge of L_0 with a 4-cycle. Then the Laakso graph L_(n+1) is obtained from L_n by replacing each edge {uv} in L_n with a copy of the graph L_1, where u and v are identified with the vertices of degree 1 in L_1.

Examples

			The order 1 Laakso graph L_1 has 6 vertices and 6 edges. L_(n+1) is obtained from L_n by replacing each edge in L_n with a copy of L_1. This gives us 6 vertices, then 30, then 174, and so on.
		

Crossrefs

Equals twice A152596.

Programs

  • Mathematica
    LinearRecurrence[{7,-6},{6,30},30] (* Paolo Xausa, Oct 16 2023 *)

Formula

a(n) = a(n-1) + 4*6^(n-1).
a(n) = (2/5) * (2*6^n+3). - Christian Krause, Sep 30 2023