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
KEYWORD
nonn,easy,less
AUTHOR
Juri-Stepan Gerasimov, Mar 06 2010
EXTENSIONS
Corrected by Charles R Greathouse IV, Mar 23 2010
STATUS
approved