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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A307544 Irregular triangle read by rows: T(n,k) = A087207(A307540(n,k)). 1
0, 1, 3, 2, 7, 5, 6, 4, 15, 11, 13, 9, 14, 10, 12, 8, 31, 23, 27, 19, 29, 21, 25, 30, 17, 22, 26, 18, 28, 20, 24, 16, 63, 47, 55, 59, 39, 43, 51, 61, 35, 45, 53, 57, 37, 62, 41, 49, 46, 54, 33, 58, 38, 42, 50, 60, 34, 44, 52, 56, 36, 40, 48, 32, 127, 95, 111, 119 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Let gpf(m) = A006530(m) and let phi(m) = A000010(m) for m in A005117.

Row n contains m in A005117 such that A006530(m) = n, sorted such that phi(m)/m increases as k increases.

Let m be the squarefree kernel A007947(m') of m'. We only consider squarefree m since phi(m)/m = phi(m')/m'. Let prime p | n and prime q be a nondivisor of n.

Since m is squarefree, we might encode the multiplicities of its prime divisors in a positional notation M that is finite at n significant digits. For example, m = 42 can be encoded reverse(A067255(42)) = 1,0,1,1 = 7^1 * 5^0 * 3^1 * 2^1. It is necessary to reverse row m of A067255 (hereinafter simply A067255(m)) so as to preserve zeros in M = A067255(m) pertaining to small nondivisor primes q < p. The code M is a series of 0s and 1s since m is squarefree. Then it is clear that row n contains all m such that A067255(m) has n terms, and there are 2^(n - 1) possible terms for n >= 1.

We may use an approach that generates the binary expansion of the range 2^(n - 1) < M < 2^n - 1, or we may append 1 to the reversed (n - 1)-tuples of {1, 0} (as A059894) to achieve codes M -> m for each row n.

Originally it was thought that the codes M were in order of the latter algorithm, and we could avoid sorting. Observation shows that the m still require sorting by the function phi(m)/m indeed to be in increasing order in row n. Still, the latter approach is slightly more efficient than the former in generating the sequence.

This sequence interprets the code M as a binary value. The sequence is a permutation of the natural numbers since the ratio phi(m)/m is unique for squarefree m.

This sequence and A059894 are identical for 1 <= n <= 23.

Numbers of terms in rows n of this sequence and A059894 (partitioned by powers of 2) that are coincident: 1, 2, 4, 8, 14, 14, 10, 26, 14, 20, 10, 16, 22, 12, 18, 18, 16, 14, 18, 18, 18, 14, 16, ...}.

The graphs of this sequence and A059894 are similar.

The graph of this sequence feature squares of size 2^(j-1) at (x,y) = (h,h) where h = 2^j, integers, that have pi-radian rotational symmetry.

LINKS

Michael De Vlieger, Table of n, a(n) for n = 0..16384

Michael De Vlieger, Plot comparing A059894 and A307544.

FORMULA

For n > 0, row lengths = 2^(n - 1).

T(n,1) = 2^n - 1 = A000225(n).

T(n,2^(n - 1)) = 2^(n - 1).

EXAMPLE

First terms of this sequence appear bottom to top in the chart below. The values of n appear in the header, values m = T(n,k) followed parenthetically by phi(m)/m appear in column n. In square brackets, we write the multiplicities of primes in positional order with the smallest prime at right (big-endian). The x axis plots k according to primepi(gpf(m)), while the y axis plots k according to phi(m)/m:

    0       1          2             3             4

    .       .          .             .             .

--- 1 ------------------------------------------------

  (1/1)     .          .             .             .

   [0]      .          .             .             .

    .       .          .             .             .

    .       .          .             .             7

    .       .          .             5           (6/7)

    .       .          .           (4/5)        [1000]

    .       .          .           [100]           .

    .       .          .             .            35

    .       .          3             .          (24/35)

    .       .        (2/3)           .          [1100]

    .       .        [10]            .             .

    .       .          .             .             .

    .       .          .             .            21

    .       .          .             .           (4/7)

    .       .          .            15          [1010]

    .       .          .          (8/15)           .

    .       2          .           [110]           .

    .     (1/2)        .             .             .

    .      [1]         .             .            105

    .       .          .             .          (16/35)

    .       .          .             .          [1110]

    .       .          .             .            14

    .       .          .            10           (3/7)

    .       .          .           (2/5)        [1001]

    .       .          .           [101]           .

    .       .          .             .            70

    .       .          6             .          (12/35)

    .       .        (1/3)           .          [1101]

    .       .        [11]            .            42

    .       .          .            30           (2/7)

    .       .          .          (4/15)        [1011]

    .       .          .           [111]          210

    .       .          .             .           (8/35)

    .       .          .             .          [1111]

...

a(1) = 0 since T(0,1) = 1 = empty product.

a(2) = 1 since T(1,1) = 2 = 2^1 -> binary "1" = decimal 1.

a(3) = 3 since T(2,1) = 6 = 2^1 * 3^1 -> binary "11" = decimal 3.

a(4) = 2 since T(2,2) = 3 = 2^0 * 3^1 -> binary "10" = decimal 2.

a(5) = 7 since T(3,1) = 30 = 2^1 * 3^1 * 5^1 -> binary "111" = decimal 7, etc.

Graph of first 32 terms: (Begin)

              x

                       x

                   x

                           x

                 x

                         x

                     x

                x

                             x

                        x

                    x

                            x

                  x

                          x

                      x

                              x

       x

           x

         x

             x

        x

            x

          x

              x

   x

     x

    x

      x

x

  x

x

(End)

MATHEMATICA

Prepend[Array[SortBy[#, Last] &@ Map[{#2, EulerPhi[#1]/#1} & @@ {Times @@  MapIndexed[Prime[First@ #2]^#1 &, Reverse@ #], FromDigits[#, 2]} &, Map[Prepend[Reverse@ #, 1] &, Tuples[{1, 0}, # - 1]]] &, 7], {{0, 0, 1}}][[All, All, 1]] // Flatten

CROSSREFS

Cf. A000010, A000040, A000079, A000225, A002110, A005117, A006094, A006530, A007947, A048672, A059894, A067255, A087207, A225679, A225680, A306237, A307540.

Sequence in context: A303076 A298847 A059894 * A126314 A200714 A086702

Adjacent sequences:  A307541 A307542 A307543 * A307545 A307546 A307547

KEYWORD

nonn,easy,look,tabf

AUTHOR

Michael De Vlieger, Apr 19 2019

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 November 20 02:34 EST 2019. Contains 329323 sequences. (Running on oeis4.)