OFFSET
1,1
LINKS
T. D. Noe, Table of n, a(n) for n=1..1000
EXAMPLE
19 = 2*3*3 + 1.
31 = 2*3*5 + 1.
MATHEMATICA
Select[Prime[Range[3, 500]], FactorInteger[(# - 1)/2][[1, 1]] > 2 && Sum[FactorInteger[(# - 1)/2][[i, 2]], {i, 1, Length[FactorInteger[(# - 1)/2]]}] == 2 &] (* Stefan Steinerberger, Sep 26 2007 *)
Take[ Select[ Sort[ Flatten[ Table[ 2Prime[p]Prime[q] + 1, {p, 47}, {q, p}]]], PrimeQ[ # ] &], 50] (* Robert G. Wilson v, Apr 06 2005 *)
Select[Prime[Range[19, 500]], OddQ[ (#-1)/2]&&3==Plus@@Last/@FactorInteger[ #-1]&] (* Zak Seidov, Sep 26 2007 *)
With[{upto=Prime[250]}, Select[2#[[1]]#[[2]]+1&/@Tuples[Prime[Range[2, upto/6]], 2], PrimeQ[#]&&#<=upto&]]//Union (* Harvey P. Dale, Apr 21 2019 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Giovanni Teofilatto, Mar 31 2005
EXTENSIONS
Edited, corrected and extended by Robert G. Wilson v, Apr 06 2005
STATUS
approved