A134201 Number of rigid hypergroups of order n.

1, 2, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6

Offset

1,2

Comments

a(n) is also the number of I-toothpicks added to the structure of the cellular automaton of A323646 when starts its n-th cycle. Column 1 of triangle A323647. - Omar E. Pol, Nov 25 2019

Also decimal expansion of 19/15. - Stefano Spezia, Mar 23 2022

References

R. Bayon and N. Lygeros, Hyperstructures and Automorphism Groups, submitted.

F. Marty, Sur une généralisation de la notion de groupe. In Proc. 8th Congr. des Mathématiciens Scandinaves, Stockholm, pp. 45-49, 1934.

Th. Vougiouklis, The fundamental relation in hyperrings: The general hyperfield, Fourth Int. Congress Algebraic Hyperstructures and Appl. (AHA), 1991, pp. 203-211.

Links

Table of n, a(n) for n=1..87.

Index entries for linear recurrences with constant coefficients, signature (1).

Formula

a(1) = 1, a(2) = 2, a(n) = 6 for n > 2.

G.f.: x*(1 + x + 4*x^2)/(1 - x). - Stefano Spezia, Mar 23 2022

E.g.f.: 6*exp(x) - 6 - 5*x - 2*x^2. - Elmo R. Oliveira, Aug 09 2024

Mathematica

Array[If[# <= 2, #, 6] &, 105] (* Michael De Vlieger, Dec 01 2019 *)

Crossrefs

Cf. A108089, A132590, A134202, A323646, A323647.

Sequence in context: A259311 A141624 A134413 * A184408 A184409 A137479

Adjacent sequences: A134198 A134199 A134200 * A134202 A134203 A134204

Keyword

nonn,easy

Author

Roman Bayon (roman.bayon(AT)gmail.com), Oct 14 2007

Status

approved