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A309072 a(n) is the concatenation of the initial digit of A247476(k) for k = A309063(n)..A309063(n+1)-1. 2
12132453674859161724822942, 121121, 121121, 2342536434553643455364345536436553789651617788966917178682392737988131273298, 78912142738493, 912112112192, 121121, 121121, 121121, 121121, 121121, 121121, 121121, 121121, 121121, 121121, 121121, 121121, 121121 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For any n > 0:

- a(n) has an even number of digits,

- for any digit d appearing in a(n):

    - d appears an even number of times,

    - each pair of digits d is separated by d other digits,

- a(n) cannot be split into two parts with these properties.

The distribution of the first million values is as follows:

  Freq.   Length   Value

  ------  -------  --------------------------------------------------------------

  932062        6                                                          121121

   44451       38                          78912142778498923727318198971711218297

   19557       12                                                    891211211819

    3915       12                                                    912112112192

       3       14                                                  78912142738493

       1       26                                      12132453674859161724822942

       1       76  234253643455364345536434553643..966917178682392737988131273298

       1      280  789121427784989237213188991211..392931211212392931211212392131

       1      712  121322432234223322432234223322..819191717881219277988131273298

       1     2200  789121427784989237213188991211..392931211212392931211212392131

       1     6438  121322432234223322432234223322..798916167718196687792562387539

       1    64958  121322432234223322432234223322..819191717881219277988131273298

       1   112810  678912162768798916167718196687..687989161677181968971711218297

       1   563478  121322432234223322432234223322..177669883476364987896612172869

       1   744654  678912162768798916167718196687..819191717881219277988131273298

       1  2095732  789121427784989237273181989712..392931211212392931211212392131

       1  5830936  234253243252332243223422332243..177669883476364987896612172869

LINKS

Table of n, a(n) for n=1..19.

Rémy Sigrist, C program for A309072

EXAMPLE

For n = 2:

- A309063(2) = 27 and A309063(3)-1 = 32,

- A000030(A247476(27)) = A000030(13) = 1,

- A000030(A247476(28)) = A000030(25) = 2,

- A000030(A247476(29)) = A000030(14) = 1,

- A000030(A247476(30)) = A000030(15) = 1,

- A000030(A247476(31)) = A000030(26) = 2,

- A000030(A247476(32)) = A000030(16) = 1,

- hence a(2) = 121121.

PROG

(C) See Links section.

CROSSREFS

Cf. A000030, A247476, A309063.

Sequence in context: A280347 A009190 A095444 * A217416 A133849 A324208

Adjacent sequences:  A309069 A309070 A309071 * A309073 A309074 A309075

KEYWORD

nonn,base

AUTHOR

Rémy Sigrist, Jul 10 2019

STATUS

approved

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Last modified February 18 09:15 EST 2020. Contains 332011 sequences. (Running on oeis4.)