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A050608 Numbers n such that base 7 expansion matches (0|1|2|3)*((0|1|2)(4|5|6))?(0|1|2|3)* 4

%I

%S 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,28,29,

%T 30,31,35,36,37,38,42,43,44,45,49,50,51,52,53,54,55,56,57,58,59,60,61,

%U 62,63,64,65,66,67,68,69,70,71,72,73,77,78,79,80,84,85,86,87,91,92,93,94,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113

%N Numbers n such that base 7 expansion matches (0|1|2|3)*((0|1|2)(4|5|6))?(0|1|2|3)*

%C 49 does not divide C(2s-1,s) = A001700[ s ] (nor C(2s,s) = A000984[ s ], central column of Pascal's Triangle) if and only if s is one of the terms in this sequence.

%H <a href="/index/Ar#7-automatic">Index entries for 7-automatic sequences</a>.

%o (Perl) For conv_x_base_n function, see A050607.

%o (Perl) for($i=1; $i <= 1000; $i++) { if(("0" . conv_x_base_n($i,7)) =~ /^(0|1|2|3)*((0|1|2)(4|5|6))?(0|1|2|3)*$/) { print $i, ","; } }

%Y Cf. A037461, A046097, A050607.

%K nonn,easy,base

%O 1,2

%A Antti Karttunen, 1999

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Last modified June 15 04:47 EDT 2021. Contains 345043 sequences. (Running on oeis4.)