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A174047 Numbers k such that exactly one of 2*k-1 and 2*k+1 is prime. 1
1, 4, 5, 7, 8, 10, 11, 12, 14, 16, 18, 19, 20, 22, 23, 24, 26, 27, 29, 31, 33, 34, 35, 37, 39, 40, 41, 42, 44, 45, 48, 49, 50, 52, 53, 55, 56, 57, 63, 64, 65, 66, 68, 70, 74, 76, 78, 79, 81, 82, 83, 84, 86, 87, 89, 91, 95, 97, 98, 100, 105, 106, 111, 112, 113, 115, 116, 117, 119, 121, 125, 126, 128, 129, 131 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1)=1 because 2*1-1=1 is nonprime and 2*1+1=3 is prime.

MAPLE

P:= [seq(ithprime(i), i=2..100)]:

PD:= P[2..-1]-P[1..-2]:

Q:= select(t -> PD[t]<>2, [$1..98]):

1, op(map(i -> ((P[i]+1)/2, (P[i+1]-1)/2), Q)); # Robert Israel, May 06 2019

MATHEMATICA

Select[Range[150], Sort[PrimeQ[2 #+{1, -1}]]=={False, True}&] (* Harvey P. Dale, Aug 21 2013 *)

CROSSREFS

Sequence in context: A276705 A168044 A248188 * A285085 A231507 A097482

Adjacent sequences:  A174044 A174045 A174046 * A174048 A174049 A174050

KEYWORD

nonn,easy,less

AUTHOR

Juri-Stepan Gerasimov, Mar 06 2010

EXTENSIONS

Corrected by Charles R Greathouse IV, Mar 23 2010

STATUS

approved

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Last modified July 16 12:04 EDT 2020. Contains 335788 sequences. (Running on oeis4.)