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A174392 Neither n-1 nor n+1 is prime. 0
0, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 26, 27, 29, 31, 33, 34, 35, 37, 39, 41, 43, 45, 47, 49, 50, 51, 53, 55, 56, 57, 59, 61, 63, 64, 65, 67, 69, 71, 73, 75, 76, 77, 79, 81, 83, 85, 86, 87, 89, 91, 92, 93, 94, 95, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 116, 117, 118 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that n-+1 are both nonprime. Zero together with inverse hyperbolic cotangent reducible numbers.

Union of {0} and A099047. [From R. J. Mathar, Aug 09 2010]

LINKS

Table of n, a(n) for n=1..69.

EXAMPLE

a(1)=0 because 0-1=-1 and 0+1=1 are nonprime; a(2)=5 because 5-1=4 and 5+1=6 are nonprime.

MATHEMATICA

Select[Range[0, 150], !PrimeQ[#-1]&&!PrimeQ[#+1]&] (* Harvey P. Dale, Aug 15 2012 *)

Join[{0}, Mean/@SequencePosition[Table[If[PrimeQ[n], 0, 1], {n, 200}], {1, x_, 1}]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Nov 17 2019 *)

CROSSREFS

Cf. A084926.

Sequence in context: A106505 A097985 A099047 * A084926 A333038 A049013

Adjacent sequences:  A174389 A174390 A174391 * A174393 A174394 A174395

KEYWORD

nonn,easy

AUTHOR

Juri-Stepan Gerasimov, Mar 18 2010

EXTENSIONS

Corrected by Charles R Greathouse IV, Mar 18 2010

STATUS

approved

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Last modified September 25 23:23 EDT 2020. Contains 337346 sequences. (Running on oeis4.)