OFFSET
0,3
COMMENTS
This permutation has only finite cycles: numbers 0, 1, 2, 3, ... are in the cycles of size: 1, 1, 1, 2, 2, 4, 4, 4, 4, 4, 4, 4, 1, 4, 4, 4, 4, 4, 4, 4, 3, 3, 4, 4, 3, 4, 4, 4, 4, 4, 2, 4, 4, 4, 4, 5, 5, 1, 4, 4, 5, 4, 5, 4, 4, 2, 4, 4, 5, 4, 4, 4, 4, 4, 4, 4, 2, 4, 4, 4, 7, 4, 4, 7, 4, 4, 4, 4, 4, 4, 7, 3, 7, 3, 1, ...
The first number with cycle size 1 (i.e., fixed point) is 0, the first in a 2-cycle is 3 (as a(3) = 4, a(4) = 3), the first in 3-cycle is 20, the first in 4-cycle is 5, the first in 5-cycle is 35, in 6-cycle 213, in 7-cycle 60, in 8-cycle and 9-cycle (no terms among 0..10080), the first in 10-cycle: 447, the first in 12-cycle: 220, in 14-cycle: 843, in 15-cycle: 2485, in 20-cycle: 385.
LINKS
FORMULA
As a recurrence:
a(0)=0, a(1)=1, a(2)=2,
a(3*n) = 4*a(n),
a(8*n) = 5*a(n),
a(4*n) = 3*a(n) [when n is odd],
a(14*n) = 9*a(n),
a(49*n) = 27*a(n),
a(7*n) = 6*a(n) [when n is odd and not divisible by 7],
a(p_i) = p_{a(i)} for primes whose index i is neither 2 nor 4 [primes other than 3 or 7],
and
a(u * v) = a(u) * a(v) for other composite cases.
PROG
;; Alternative implementation based on the given direct recurrence. Needs Antti Karttunen's IntSeq-library:
(definec (A235485 n) (cond ((< n 3) n) ((zero? (modulo n 3)) (* 4 (A235485 (/ n 3)))) ((zero? (modulo n 8)) (* 5 (A235485 (/ n 8)))) ((zero? (modulo n 4)) (* 3 (A235485 (/ n 4)))) ((zero? (modulo n 14)) (* 9 (A235485 (/ n 14)))) ((zero? (modulo n 49)) (* 27 (A235485 (/ n 49)))) ((zero? (modulo n 7)) (* 6 (A235485 (/ n 7)))) ((= 1 (A010051 n)) (A000040 (A235485 (A000720 n)))) (else (reduce * 1 (map A235485 (ifactor n))))))
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jan 11 2014
EXTENSIONS
Name and incorrect claim about multiplicativity corrected by Antti Karttunen, Feb 12 2018
STATUS
approved