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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.

%I A246398 #7 Nov 13 2014 23:57:14
%S A246398 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,
%T A246398 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,
%U A246398 1,1,1,0,1,0,1,1,1,0,1,0,1,1,1,0,2,1
%N A246398 Smallest number of digits that have to be inserted into or prepended to decimal representation of n, to get a prime.
%C A246398  a(n) = 0 iff n is a prime number, a(A000040(n)) = 0;
%C A246398 a(n) = A055642(A062584(n)) - A055642(n).
%H A246398 Reinhard Zumkeller, <a href="/A246398/b246398.txt">Table of n, a(n) for n = 0..10000</a>
%o A246398 (Haskell)
%o A246398 a246398 n = a246398_list !! n
%o A246398 a246398_list = f 0 $ map show a000040_list where
%o A246398    f x pss = (length ps - length xs) :
%o A246398              f (x + 1) (dropWhile (== xs) pss)
%o A246398      where ps = head [qs | qs <- pss, isin xs qs]; xs = show x
%o A246398    isin [] _  = True
%o A246398    isin _  [] = False
%o A246398    isin (u:us) vs = not (null ws) && isin us ws
%o A246398                     where ws = dropWhile (/= u) vs
%Y A246398 Cf. A000040, A055642, A062584, A068164.
%K A246398 nonn,base
%O A246398 0,1
%A A246398 _Reinhard Zumkeller_, Nov 13 2014