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A085271 Difference between n-th composite number and its smallest prime divisor.

%I A085271 #16 Jun 20 2019 17:40:40
%S A085271 2,4,6,6,8,10,12,12,14,16,18,18,20,22,20,24,24,26,28,30,30,32,30,34,
%T A085271 36,36,38,40,42,42,44,46,42,48,48,50,52,50,54,54,56,58,60,60,62,60,64,
%U A085271 66,66,68,70,72,72,74,70,76,78,78,80,82,80,84,84,86,88,84,90,90,92,90,94
%N A085271 Difference between n-th composite number and its smallest prime divisor.
%e A085271 For composite number 91 we have 91-7 = 84.
%t A085271 #-FactorInteger[#][[1,1]]&/@Complement[Range[2,200],Prime[Range[PrimePi[200]]]] (* _Harvey P. Dale_, Dec 11 2010 *)
%t A085271 #-Divisors[#][[2]]&/@Select[Range[4,200],!PrimeQ[#]&] (* _Zak Seidov_, Apr 09 2011 *)
%o A085271 (PARI) cminusp(n) = { for(x=2,n, forprime(p=2,floor(sqrt(x)), if(x%p==0,print1(x-p,","); break); ) ) }
%o A085271 (PARI){n=200;for(x=4,n,if(isprime(x),,print1(x-divisors(x)[2], ", ")))} \\ _Zak Seidov_, Apr 09 2011
%Y A085271 Cf. A002808, A085273.
%K A085271 easy,nonn
%O A085271 1,1
%A A085271 _Cino Hilliard_, Aug 12 2003
%E A085271 Typo in data corrected by _Zak Seidov_, Apr 09 2011