cp's OEIS Frontend

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").

%I A362987 #19 May 20 2023 14:46:29
%S A362987 10,11,12,21,23,13,20,32,24,14,34,25,31,22,30,35,42,15,43,26,36,37,46,
%T A362987 16,41,45,53,57,47,33,52,27,40,64,54,38,48,58,68,17,63,28,69,18,51,39,
%U A362987 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 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").
%C A362987 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 A362987 a(1) = 10 with spread 1;
%e A362987 a(2) = 11 with spread 0;
%e A362987 a(3) = 12 with spread 1;
%e A362987 a(4) = 21 with spread 1;
%e A362987 a(5) = 23 with spread 1;
%e A362987 a(6) = 13 with spread 2; etc.
%e A362987 We see that the above succession of spreads is the digits' succession of S.
%t A362987 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 A362987 Cf. A100787.
%K A362987 base,nonn
%O A362987 1,1
%A A362987 _Eric Angelini_, May 12 2023