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

1,1

Links

Table of n, a(n) for n=1..71.

Example

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

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 *)

Prog

(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

Crossrefs

Cf. A002808, A085273.

Sequence in context: A050827 A082990 A099188 * A347376 A260812 A003972

Adjacent sequences: A085268 A085269 A085270 * A085272 A085273 A085274

Keyword

easy,nonn

Author

Cino Hilliard, Aug 12 2003

Extensions

Typo in data corrected by Zak Seidov, Apr 09 2011

Status

approved