cp's OEIS Frontend

A309072 a(n) is the concatenation of the initial digit of A247476(k) for k = A309063(n)..A309063(n+1)-1.

%I A309072 #8 Jul 11 2019 15:47:27
%S A309072 12132453674859161724822942,121121,121121,
%T A309072 2342536434553643455364345536436553789651617788966917178682392737988131273298,
%U A309072 78912142738493,912112112192,121121,121121,121121,121121,121121,121121,121121,121121,121121,121121,121121,121121,121121
%N A309072 a(n) is the concatenation of the initial digit of A247476(k) for k = A309063(n)..A309063(n+1)-1.
%C A309072 For any n > 0:
%C A309072 - a(n) has an even number of digits,
%C A309072 - for any digit d appearing in a(n):
%C A309072     - d appears an even number of times,
%C A309072     - each pair of digits d is separated by d other digits,
%C A309072 - a(n) cannot be split into two parts with these properties.
%C A309072 The distribution of the first million values is as follows:
%C A309072   Freq.   Length   Value
%C A309072   ------  -------  --------------------------------------------------------------
%C A309072   932062        6                                                          121121
%C A309072    44451       38                          78912142778498923727318198971711218297
%C A309072    19557       12                                                    891211211819
%C A309072     3915       12                                                    912112112192
%C A309072        3       14                                                  78912142738493
%C A309072        1       26                                      12132453674859161724822942
%C A309072        1       76  234253643455364345536434553643..966917178682392737988131273298
%C A309072        1      280  789121427784989237213188991211..392931211212392931211212392131
%C A309072        1      712  121322432234223322432234223322..819191717881219277988131273298
%C A309072        1     2200  789121427784989237213188991211..392931211212392931211212392131
%C A309072        1     6438  121322432234223322432234223322..798916167718196687792562387539
%C A309072        1    64958  121322432234223322432234223322..819191717881219277988131273298
%C A309072        1   112810  678912162768798916167718196687..687989161677181968971711218297
%C A309072        1   563478  121322432234223322432234223322..177669883476364987896612172869
%C A309072        1   744654  678912162768798916167718196687..819191717881219277988131273298
%C A309072        1  2095732  789121427784989237273181989712..392931211212392931211212392131
%C A309072        1  5830936  234253243252332243223422332243..177669883476364987896612172869
%H A309072 Rémy Sigrist, <a href="/A309072/a309072.txt">C program for A309072</a>
%e A309072 For n = 2:
%e A309072 - A309063(2) = 27 and A309063(3)-1 = 32,
%e A309072 - A000030(A247476(27)) = A000030(13) = 1,
%e A309072 - A000030(A247476(28)) = A000030(25) = 2,
%e A309072 - A000030(A247476(29)) = A000030(14) = 1,
%e A309072 - A000030(A247476(30)) = A000030(15) = 1,
%e A309072 - A000030(A247476(31)) = A000030(26) = 2,
%e A309072 - A000030(A247476(32)) = A000030(16) = 1,
%e A309072 - hence a(2) = 121121.
%o A309072 (C) See Links section.
%Y A309072 Cf. A000030, A247476, A309063.
%K A309072 nonn,base
%O A309072 1,1
%A A309072 _Rémy Sigrist_, Jul 10 2019