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A096870 Difference between the n-th repunit and the previous prime. 4

%I

%S 4,2,2,18,2,20,10,2,14,52,8,18,58,58,72,4,20,74,84,58,14,18,82,168,28,

%T 50,168,84,8,138,112,82,2,28,2,62,34,50,74,24,8,54,204,22,428,40,118,

%U 200,72,40,30,42,284,44,114,268,80,18,4,74,142,182,140,112,214,152,90

%N Difference between the n-th repunit and the previous prime.

%H Robert Israel, <a href="/A096870/b096870.txt">Table of n, a(n) for n = 2..1000</a>

%F a(n) = A002275(n) - A096498(n) = A096499(n) - A096869(n).

%p f:= proc(n) local r; r:= (10^n-1)/9; r - prevprime(r) end proc:

%p map(f, [$2..100]); # _Robert Israel_, Feb 23 2017

%t PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; Table[(10^n - 1)/9 - PrevPrim[(10^n - 1)/9], {n, 2, 70}]

%t Table[With[{ru=(10^n-1)/9},ru-NextPrime[ru,-1]],{n,2,70}] (* _Harvey P. Dale_, Aug 14 2011 *)

%Y Cf. A096869.

%K nonn

%O 2,1

%A _Robert G. Wilson v_, Jul 12 2004

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Last modified August 22 16:17 EDT 2019. Contains 326178 sequences. (Running on oeis4.)