A123398 Topswops: number of permutations of cards achieving A000375(n).

1, 1, 2, 2, 1, 5, 2, 1, 1, 1, 1, 1, 1, 4, 6, 1, 2, 1, 4, 1, 5

Offset

1,3

References

D. E. Knuth, TAOCP, Section 7.2.1.2, Problems 107-109.

Links

Table of n, a(n) for n=1..21.

Benjamin Chaffin, Longest Topswops decks for sizes 20 and 21

Kento Kimura, Atsuki Takahashi, Tetsuya Araki, and Kazuyuki Amano, Maximum Number of Steps of Topswops on 18 and 19 Cards, arXiv:2103.08346 [cs.DM], 2021.

Yuichi Komano and Takaaki Mizuki, Physical Zero-Knowledge Proof Protocol for Topswops, Int'l Conf. Info. Sec. Practice and Experience (ISPEC 2022) Lecture Notes in Comp. Sci. book series (LNCS Vol. 13620) Springer, Cham, 537-553.

Crossrefs

Cf. A000375.

Sequence in context: A326933 A394734 A379756 * A277495 A188945 A396668

Adjacent sequences: A123395 A123396 A123397 * A123399 A123400 A123401

Keyword

nonn,more

Author

N. J. A. Sloane, Oct 15 2006

Extensions

Added a(17)=2 using comments in A000375 from Quan T. Nguyen, William Fahle; by Moritz Franckenstein, Nov 27 2010

a(18)-a(19) from Kimura et al. added by Andrey Zabolotskiy, Mar 24 2021

a(20)-a(21) from Benjamin Chaffin, May 02 2026

Status

approved