A013927 - OEIS

A013927

Begin with 2n cards in n piles of 2, the piles being {1,1},{2,2},{3,3},...,{n,n}. How many transpositions of adjacent (single) cards are needed to reverse the order of the piles?

0, 2, 5, 10, 15, 23, 31, 40

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

REFERENCES

Graham Brightwell, Michael Littman and Peter Winkler (pw(AT)research.bell-labs.com), unpublished.

LINKS

Table of n, a(n) for n=1..8.

Bert Dobbelaere, Example solution for a(8)

EXAMPLE

From Bert Dobbelaere, Jan 19 2020: (Start)

a(3) = 5:

Start: {1,1} {2,2} {3,3}

Step 1: {2,1} {1,2} {3,3}

Step 2: {2,1} {3,2} {1,3}

Step 3: {2,3} {1,2} {1,3}

Step 4: {2,3} {3,2} {1,1}

Step 5: {3,3} {2,2} {1,1}

(End)

CROSSREFS

Sequence in context: A179207 A008822 A267454 * A163059 A099738 A064513

Adjacent sequences: A013924 A013925 A013926 * A013928 A013929 A013930

KEYWORD

nonn,more

AUTHOR

N. J. A. Sloane

EXTENSIONS

a(7)-a(8) from Bert Dobbelaere, Jan 19 2020

STATUS

approved