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

2, 4, 6, 6, 8, 10, 12, 12, 14, 16, 18, 18, 20, 22, 20, 24, 24, 26, 28, 30, 30, 32, 30, 34, 36, 36, 38, 40, 42, 42, 44, 46, 42, 48, 48, 50, 52, 50, 54, 54, 56, 58, 60, 60, 62, 60, 64, 66, 66, 68, 70, 72, 72, 74, 70, 76, 78, 78, 80, 82, 80, 84, 84, 86, 88, 84, 90, 90, 92, 90, 94

Offset: 1

Author

Cino Hilliard, Aug 12 2003

Keywords

• easy
• nonn

Examples

			For composite number 91 we have 91-7 = 84.
		

Crossrefs

Cf. A002808, A085273.

Programs

Mathematica

#-FactorInteger[#][[1,1]]&/@Complement[Range[2,200],Prime[Range[PrimePi[200]]]] (* Harvey P. Dale, Dec 11 2010 *)
#-Divisors[#][[2]]&/@Select[Range[4,200],!PrimeQ[#]&] (* Zak Seidov, Apr 09 2011 *)

PARI

cminusp(n) = { for(x=2,n, forprime(p=2,floor(sqrt(x)), if(x%p==0,print1(x-p,","); break); ) ) }

PARI

{n=200;for(x=4,n,if(isprime(x),,print1(x-divisors(x)[2], ", ")))} \\ Zak Seidov, Apr 09 2011

Extensions

Typo in data corrected by Zak Seidov, Apr 09 2011