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A094870
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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.
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2
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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, 28, 27, 29, 36, 32, 31, 33, 39, 38, 34, 41, 30, 37, 35, 44, 48, 42, 40, 43, 50, 46, 52, 47, 45, 54, 49, 56, 58, 57, 51, 61, 53, 59, 63, 60, 68, 64, 62, 70, 55, 65, 67, 73, 69, 83, 76
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| 3n/8 <= a(n) < 3n/2 (P. Hegarty). Conjecture: lim_{n->infinity} a(n)/n = 1 (P. Hegarty).
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LINKS
| Peter Hegarty, Permutations avoiding arithmetic patterns, The Electronic Journal of Combinatorics, 11 (2004), #R39.
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EXAMPLE
| a(3)=4 because it can't be 1=a(1), 2=a(2) and 3=2*a(3-1)-a(3-2).
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MAPLE
| 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);
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CROSSREFS
| Sequence in context: A107897 A133256 A095690 * A075618 A095689 A083194
Adjacent sequences: A094867 A094868 A094869 * A094871 A094872 A094873
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KEYWORD
| easy,nonn
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AUTHOR
| Alec Mihailovs (alec(AT)mihailovs.com), Jun 16 2004
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