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A246398
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Smallest number of digits that have to be inserted into or prepended to decimal representation of n, to get a prime.
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1
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2, 1, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 2, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 2, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 2, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 2, 1
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OFFSET
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0,1
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COMMENTS
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a(n) = 0 iff n is a prime number, a(A000040(n)) = 0;
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LINKS
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PROG
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(Haskell)
a246398 n = a246398_list !! n
a246398_list = f 0 $ map show a000040_list where
f x pss = (length ps - length xs) :
f (x + 1) (dropWhile (== xs) pss)
where ps = head [qs | qs <- pss, isin xs qs]; xs = show x
isin [] _ = True
isin _ [] = False
isin (u:us) vs = not (null ws) && isin us ws
where ws = dropWhile (/= u) vs
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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