cp's OEIS Frontend

A336954 Lexicographically earliest sequence of distinct positive terms such that, in the concatenation of the decimal representations of the terms, for any digit d at position p, d appears at some position q such that abs(p-q) = d.

%I A336954 #19 Aug 20 2025 10:34:06
%S A336954 1,10,2,3,20,30,4,5,6,7,40,50,60,70,8,9,11,12,32,83,90,22,220,21,13,
%T A336954 33,333,23,24,25,34,43,52,42,26,27,28,36,63,71,18,61,14,29,240,31,130,
%U A336954 91,15,35,53,54,55,44,37,430,41,17,45,38,93,51,16,48,49,46
%N A336954 Lexicographically earliest sequence of distinct positive terms such that, in the concatenation of the decimal representations of the terms, for any digit d at position p, d appears at some position q such that abs(p-q) = d.
%C A336954 This sequence combines features of A322467 and of A336880.
%C A336954 Some numbers, like 121, cannot appear in this sequence.
%H A336954 Rémy Sigrist, <a href="/A336954/b336954.txt">Table of n, a(n) for n = 1..10000</a>
%H A336954 Rémy Sigrist, <a href="/A336954/a336954.gp.txt">PARI program for A336954</a>
%e A336954 For n = 1:
%e A336954 - we can choose a(1) = 1.
%e A336954 For n = 2:
%e A336954 - a(2) must start with a digit 1,
%e A336954 - we can choose a(2) = 10.
%e A336954 For n = 3:
%e A336954 - we can choose a(3) = 2.
%e A336954 For n = 4:
%e A336954 - we can choose a(4) = 3.
%e A336954 For n = 5:
%e A336954 - a(5) must start with a digit 2,
%e A336954 - we can choose a(5) = 20.
%o A336954 (PARI) \\ See Links section.
%Y A336954 Cf. A322467, A336880.
%K A336954 nonn,base
%O A336954 1,2
%A A336954 _Rémy Sigrist_, Aug 08 2020