0,3

This automorphism rotates by 180 degrees the interpretation n (the non-crossing handshakes) of Stanley's exercise 19.

Table of n, a(n) for n=0..70.

A. Karttunen, Gatomorphisms (Includes the complete Scheme program for computing this sequence)

R. P. Stanley, Exercises on Catalan and Related Numbers

Index entries for sequences that are permutations of the natural numbers

(Scheme function implementing this automorphism on list-structures:) (define (RotateHandshakes180 a) (RotateHandshakes_n_steps a (count-pars a)))

(define (count-pars a) (if (not (pair? a)) 0 (+ 1 (count-pars (car a)) (count-pars (cdr a)))))

(define (RotateHandshakes a) (if (null? a) (list) (append (car a) (list (cdr a)))))

(define (RotateHandshakes_n_steps a n) (if (zero? n) a (RotateHandshakes_n_steps (RotateHandshakes a) (-1+ n))))

Cf. A057501, A069772, A069888, A069889.

Sequence in context: A318739 A205299 A222242 * A235801 A076986 A225403

Adjacent sequences: A069768 A069769 A069770 * A069772 A069773 A069774

nonn

Antti Karttunen, Apr 16 2002

approved