A066246 - OEIS

%I #21 Aug 21 2024 17:10:50

%S 0,0,0,1,0,2,0,3,4,5,0,6,0,7,8,9,0,10,0,11,12,13,0,14,15,16,17,18,0,

%T 19,0,20,21,22,23,24,0,25,26,27,0,28,0,29,30,31,0,32,33,34,35,36,0,37,

%U 38,39,40,41,0,42,0,43,44,45,46,47,0,48,49,50,0,51,0,52,53,54,55,56,0,57

%N a(n) = 0 unless n is a composite number A002808(k) then a(n) = k.

%H Charles R Greathouse IV, <a href="/A066246/b066246.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A239968(n) + A010051(n) - 1. - _Reinhard Zumkeller_, Mar 30 2014

%t Module[{k=1},Table[If[CompositeQ[n],k;k++,0],{n,100}]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 03 2019 *)

%o (PARI) a(n)=if(isprime(n),0,max(0,n-primepi(n)-1)) \\ _Charles R Greathouse IV_, Aug 21 2011

%o (Haskell)

%o import Data.List (unfoldr, genericIndex)

%o a066246 n = genericIndex a066246_list (n - 1)

%o a066246_list = unfoldr x (1, 1, a002808_list) where

%o    x (i, z, cs'@(c:cs)) | i == c = Just (z, (i + 1, z + 1, cs))

%o                         | i /= c = Just (0, (i + 1, z, cs'))

%o -- _Reinhard Zumkeller_, Jan 29 2014

%Y Cf. A002808, A239968, A010051, A049084.

%Y Cf. A026233, A026238.

%K nonn

%O 1,6

%A _Reinhard Zumkeller_, Dec 09 2001