OFFSET
1,2
COMMENTS
n-(-1)^n is prime.
Largest nonprime<prime(n+1) or largest nonprime<n-th odd prime. [From Juri-Stepan Gerasimov, Oct 29 2009]
FORMULA
A006093 \ {2}.
EXAMPLE
k=1 is in the sequence because 1+1=2 is prime. k=4 is in the sequence because 1+4=5 is prime.
MATHEMATICA
Select[Range[300], !PrimeQ[#]&&With[{d=Divisors[#]}, PrimeQ[d[[1]]+ d[[-1]]]]&] (* Harvey P. Dale, Oct 01 2015 *)
CROSSREFS
KEYWORD
nonn,less
AUTHOR
Juri-Stepan Gerasimov, Oct 02 2009, Oct 14 2009
EXTENSIONS
Entries checked by R. J. Mathar, Oct 10 2009
STATUS
approved