A208667 Number of 2n-bead necklaces labeled with numbers 1..4 allowing reversal, with neighbors differing by exactly 1.
3, 5, 8, 14, 24, 47, 89, 187, 396, 881, 1990, 4645, 10935, 26211, 63320, 154378, 378444, 933023, 2308957, 5735372, 14286908, 35683815, 89324138, 224057919, 563033979, 1417210457, 3572641304, 9018885122, 22796905056, 57692673963, 146167385345, 370710166435
Offset: 1
Keywords
Examples
All solutions for n=4: ..1....2....2....2....1....1....1....1....1....3....1....1....2....2 ..2....3....3....3....2....2....2....2....2....4....2....2....3....3 ..1....2....2....2....1....1....3....3....3....3....3....1....4....4 ..2....3....3....3....2....2....4....2....2....4....2....2....3....3 ..1....4....2....2....3....1....3....1....3....3....3....3....2....4 ..2....3....3....3....4....2....4....2....4....4....2....2....3....3 ..1....4....2....4....3....3....3....3....3....3....3....3....4....4 ..2....3....3....3....2....2....2....2....2....4....2....2....3....3
Links
- Andrew Howroyd, Table of n, a(n) for n = 1..100
Crossrefs
Column 4 of A208671.
Formula
Extensions
a(25)-a(32) from Andrew Howroyd, Mar 19 2017