Search: id:A094870
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%I A094870
%S A094870 1,2,4,3,5,6,8,7,10,9,13,12,14,11,17,16,22,15,23,18,21,20,25,24,26,19,
%T A094870 28,27,29,36,32,31,33,39,38,34,41,30,37,35,44,48,42,40,43,50,46,52,47,
%U A094870 45,54,49,56,58,57,51,61,53,59,63,60,68,64,62,70,55,65,67,73,69,83,76
%N A094870 a(1)=1; for n>1 a(n) is the minimal positive integer t not equal to a(1), 
               ..., a(n-1) such that t-a(n-i) is not equal to a(n-i)-a(n-2i) for 
               all 1<=i<n/2.
%C A094870 3n/8 <= a(n) < 3n/2 (P. Hegarty). Conjecture: lim_{n->infinity} a(n)/
               n = 1 (P. Hegarty).
%H A094870 Peter Hegarty, <a href="http://www.combinatorics.org/Volume_11/Abstracts/
               v11i1r39.html">Permutations avoiding arithmetic patterns</a>, The 
               Electronic Journal of Combinatorics, 11 (2004), #R39.
%e A094870 a(3)=4 because it can't be 1=a(1), 2=a(2) and 3=2*a(3-1)-a(3-2).
%p A094870 A:=proc(n) option remember; local t, S, i; S:={$1..1000} minus {seq(A(i),
               i=1..n-1)}; t:=min(S[]); i:=1; while i<floor((n+1)/2) do if t-A(n-i)=A(n-i)-A(n-2*i) 
               then S:=S minus {t}; t:=min(S[]); i:=1 else i:=i+1 fi od; t end: 
               A(1):=1: seq(A(n), n=1..200);
%Y A094870 Sequence in context: A107897 A133256 A095690 this_sequence A075618 A095689 
               A083194
%Y A094870 Adjacent sequences: A094867 A094868 A094869 this_sequence A094871 A094872 
               A094873
%K A094870 easy,nonn
%O A094870 1,2
%A A094870 Alec Mihailovs (alec(AT)mihailovs.com), Jun 16 2004

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