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A246398 Smallest number of digits that have to be inserted into or prepended to decimal representation of n, to get a prime. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(n) = 0 iff n is a prime number, a(A000040(n)) = 0;

a(n) = A055642(A062584(n)) - A055642(n).

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

PROG

(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

CROSSREFS

Cf. A000040, A055642, A062584, A068164.

Sequence in context: A298426 A130068 A316825 * A051699 A007920 A127587

Adjacent sequences:  A246395 A246396 A246397 * A246399 A246400 A246401

KEYWORD

nonn,base

AUTHOR

Reinhard Zumkeller, Nov 13 2014

STATUS

approved

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Last modified August 22 02:44 EDT 2019. Contains 326169 sequences. (Running on oeis4.)