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

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Graham Brightwell, Michael Littman and Peter Winkler (pw(AT)research.bell-labs.com), unpublished.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