A079364 Composite numbers having two composite neighbors.

9, 15, 21, 25, 26, 27, 33, 34, 35, 39, 45, 49, 50, 51, 55, 56, 57, 63, 64, 65, 69, 75, 76, 77, 81, 85, 86, 87, 91, 92, 93, 94, 95, 99, 105, 111, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 129, 133, 134, 135, 141, 142, 143, 144, 145, 146, 147, 153, 154, 155

Offset

1,1

Comments

In other words, composite numbers that are not nearest-neighbors of primes. - Omar E. Pol, Jan 02 2009

Complement of A210940. - Omar E. Pol, Apr 18 2012

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Mathematica

Select[Range[6! ], !PrimeQ[ # ]&&!PrimeQ[ #-1]&&!PrimeQ[ #+1]&] (* Vladimir Joseph Stephan Orlovsky, Apr 26 2010 *)
With[{r=Complement[Range[160], Prime[Range[PrimePi[160]]]]}, Transpose[ Select[ Partition[r, 3, 1], Differences[#]=={1, 1}&]][[2]]] (* Harvey P. Dale, Feb 05 2012 *)

Prog

(Haskell)
a079364 n = a079364_list !! (n-1)
a079364_list = filter
   (\x -> a010051' (x - 1) == 0 && a010051' (x + 1) == 0) a002808_list
-- Reinhard Zumkeller, Jan 10 2013

Crossrefs

Cf. A000040, A002808, A014574, A045718.

Cf. A010051, A221309 (subsequence).

Sequence in context: A338599 A333312 A255763 * A160666 A039769 A270574

Adjacent sequences: A079361 A079362 A079363 * A079365 A079366 A079367

Keyword

nonn

Author

Reinhard Zumkeller, Feb 15 2003

Status

approved