login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A226605 Irregular array read by rows of numerators in which row n has one numerator from each irreducible cycle of n rational numbers under iteration by the 3x+1 function. (See Comments for selection and order of numerators.) 3
-1, 0, 1, -5, 1, -19, 5, 1, -65, 19, 23, 5, 7, 1, -211, -65, -73, 19, 23, 31, 1, 7, 1, -665, -211, -227, 65, -251, 73, 89, 19, 85, 101, 23, 31, 47, 5, 37, 1, 11, 1, -2059, -665, -697, 211, -745, 227, 259, 13, 251, 283, 73, 331, 89, 121, 19, 319, 17, 101, 19, 23 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

A cycle is irreducible if it is not a concatenation of copies of a shorter cycle.

The 3x+1 function T, on rational numbers in their lowest terms with a positive odd denominator, is defined by T(x) = x/2 if x's numerator is even, T(x) = (3x+1)/2 if x's numerator is odd.

Each numerator in a row is the first in the cyclic permutation with the lexicographically largest parity vector of numerators mod 2. The row lists these numerators in descending lexicographic order of the parity vectors.

The element with numerator a(n) has denominator A226606(n), as does every element in the same cycle.

a(n) is often the numerator with the least absolute value of the numerators in the cycle. a(20) and a(36) are the only exceptions in the first 7 rows.

LINKS

Geoffrey H. Morley, Rows 1..16 of array, flattened

J. C. Lagarias, The set of rational cycles for the 3x+1 problem, Acta Arith. 56 (1990), 33-53. - See Table 2.2 on page 39.

FORMULA

If v(0) to v(m-1) are the bits of A102659(n), when 2s are replaced by 0s, then a(n) = N(n)/GCD(N(n),D(n)) where D(n) = 2^m - 3^(v(0)+...+v(m-1)) and N(n) = sum_{j=0 to m-1} (2^j)(3^(v(j+1)+...+v(m-1)))v(j).

EXAMPLE

-1, 0, 1, -5, 1/5, -19/11, 5/7, 1/13, ... = A226605/A226606 for parity vectors 1, 0, 10, 110, 100, 1110, 1100, 1000, ... For example, the numerators of the rational cycle {-19/11,-23/11,-29/11,-38/11} have parity vector 1110.

CROSSREFS

There are A001037(n) terms in row n.

Sequence in context: A008971 A151335 A297174 * A055584 A193861 A193857

Adjacent sequences:  A226602 A226603 A226604 * A226606 A226607 A226608

KEYWORD

sign,frac,tabf

AUTHOR

Geoffrey H. Morley, Jun 27 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 18 09:38 EST 2019. Contains 320249 sequences. (Running on oeis4.)