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 A362987 Lexicographically earliest sequence S of distinct positive terms such that the successive digits of S are the successive spreads of S' terms (see Comments for definition of "spread"). 0

%I #19 May 20 2023 14:46:29

%S 10,11,12,21,23,13,20,32,24,14,34,25,31,22,30,35,42,15,43,26,36,37,46,

%T 16,41,45,53,57,47,33,52,27,40,64,54,38,48,58,68,17,63,28,69,18,51,39,

%U 56,60,59,65,62,49,50,74,61,29,73,70,85,96,72,75,79,81,84,44,71,95,83,105,104,19

%N Lexicographically earliest sequence S of distinct positive terms such that the successive digits of S are the successive spreads of S' terms (see Comments for definition of "spread").

%C The spread of n is the absolute difference between the leftmost digit of n and the rightmost digit of n. Spreads vary from 0 to 9.

%e a(1) = 10 with spread 1;

%e a(2) = 11 with spread 0;

%e a(3) = 12 with spread 1;

%e a(4) = 21 with spread 1;

%e a(5) = 23 with spread 1;

%e a(6) = 13 with spread 2; etc.

%e We see that the above succession of spreads is the digits' succession of S.

%t a[1]=10;a[n_]:=a[n]=Block[{k=10},While[Abs[First@#-Last@#]&@IntegerDigits[k][[{1,-1}]]!=Flatten[IntegerDigits/@Array[a,n-1]][[n]]||MemberQ[Array[a,n-1],k],k++];k];Array[a,72] (* _Giorgos Kalogeropoulos_, May 12 2023 *)

%Y Cf. A100787.

%K base,nonn

%O 1,1

%A _Eric Angelini_, May 12 2023

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Last modified September 8 17:50 EDT 2024. Contains 375753 sequences. (Running on oeis4.)