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A048991
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Write down the numbers 1,2,3,... but omit any number (such as 12 or 23 or 31 ...) which has appeared as a string earlier in the sequence.
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9
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 32, 33, 35, 36, 37, 38, 39, 40, 43, 44, 46, 47, 48, 49, 50, 54, 55, 57, 58, 59, 60, 65, 66, 68, 69, 70, 76, 77, 79, 80, 87, 88, 90, 99, 100, 102, 103, 104, 105, 106, 107, 108, 109, 110, 112
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| Invented by 10-year-old Hannah Rollman.
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..10000
Nick Hobson, Python program for this sequence
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EXAMPLE
| 12 is omitted since we see "1,2" at the beginning of the sequence; 101 is omitted because we can see "10,1[1]"; etc.
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PROG
| (Python) see Hobson link
(Haskell)
import Data.List (isInfixOf)
a048991 n = a048991_list !! (n-1)
a048991_list = f [1..] [] where
f (x:xs) ys | xs' `isInfixOf` ys = f xs ys
| otherwise = x : f xs (xs' ++ ys)
where xs' = reverse $ show x
-- Reinhard Zumkeller, Dec 05 2011
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CROSSREFS
| See A048992 for the omitted numbers.
Cf. A105390.
Sequence in context: A031996 A023753 A035332 * A131881 A053460 A065200
Adjacent sequences: A048988 A048989 A048990 * A048992 A048993 A048994
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KEYWORD
| nonn,nice,base,easy
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AUTHOR
| Bernardo Recaman (ignotus(AT)hotmail.com)
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EXTENSIONS
| Edited by Patrick De Geest, Jun 02 2003
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