login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A164276 The non-isolated nonprimes. 13
0, 1, 8, 9, 10, 14, 15, 16, 20, 21, 22, 24, 25, 26, 27, 28, 32, 33, 34, 35, 36, 38, 39, 40, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 62, 63, 64, 65, 66, 68, 69, 70, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 104, 105, 106, 110 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Non-isolated nonprimes in the sense that at least one of the two adjacent integers is also a nonprime.

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

FORMULA

A141468 \ A014574.

a(n) = n + n / log n + O(n / (log n)^2) by Brun's theorem. - Charles R Greathouse IV, Mar 15, 2011

MATHEMATICA

Select[Range[0, 100], !PrimeQ[#] && (!PrimeQ[# - 1] || !PrimeQ[# + 1]) & ] (* G. C. Greubel, Jul 07 2016 *)

PROG

(PARI) isA164276(n) = !isprime(n)&&(!isprime(n-1)||!isprime(n+1)) \\ Michael B. Porter, Feb 02 2010

CROSSREFS

Cf. A014574, A141468.

Sequence in context: A114842 A169928 A067683 * A154967 A271211 A072381

Adjacent sequences:  A164273 A164274 A164275 * A164277 A164278 A164279

KEYWORD

nonn,easy

AUTHOR

Juri-Stepan Gerasimov, Aug 11 2009

EXTENSIONS

40 added by R. J. Mathar, Aug 27 2009

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 26 17:40 EDT 2020. Contains 334630 sequences. (Running on oeis4.)