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A067581
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a(1) = 1, a(n) = smallest integer not yet in the sequence with no digits in common with a(n-1).
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7
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 22, 11, 20, 13, 24, 15, 23, 14, 25, 16, 27, 18, 26, 17, 28, 19, 30, 12, 33, 21, 34, 29, 31, 40, 32, 41, 35, 42, 36, 44, 37, 45, 38, 46, 39, 47, 50, 43, 51, 48, 52, 49, 53, 60, 54, 61, 55, 62, 57, 63, 58, 64, 59, 66, 70, 56, 71, 65, 72, 68, 73, 69
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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David W. Wilson has shown that the sequence contains every positive integer except those containing all the digits 1 through 9 (which obviously have no possible predecessor). Jun 04, 2002
a(A137857(n)) = A137857(n). - Reinhard Zumkeller, Feb 15 2008
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LINKS
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R. Zumkeller, Table of n, a(n) for n = 1..10000
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EXAMPLE
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a(14) = 13, since a(13) = 20 and all integers smaller than 13 have a digit in common with 20 or have already appeared in the sequence.
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MATHEMATICA
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f[s_List] := Block[{k = 1, id = IntegerDigits@ s[[ -1]]}, While[ MemberQ[s, k] || Intersection[id, IntegerDigits@k] != {}, k++ ]; Append[s, k]]; Nest[f, {1}, 71] [From Robert G. Wilson v, Apr 03 2009]
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PROG
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(Haskell)
import Data.List (delete, intersect); import Data.Function (on)
a067581 n = a067581_list !! (n-1)
a067581_list = 1 : f 1 [2..] where
f u vs = v : f v (delete v vs)
where v : _ = filter (null . (intersect `on` show) u) vs
-- Reinhard Zumkeller, Jul 01 2013
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CROSSREFS
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Cf. A136332.
Cf. A184992
Sequence in context: A138142 A085890 A134817 * A099469 A039112 A160015
Adjacent sequences: A067578 A067579 A067580 * A067582 A067583 A067584
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KEYWORD
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easy,nonn,base,nice
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AUTHOR
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Ulrich Schimke (ulrschimke(AT)aol.com)
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STATUS
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approved
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