OFFSET
1,1
COMMENTS
a(40) >= 1489. - Max Alekseyev, Aug 05 2019
1501, 1587, 1667, 2250, 3393, 5845, 9967, 16147 are terms of this sequence. - Chai Wah Wu, Oct 18 2019
FORMULA
EXAMPLE
199 is in this sequence because 2^199-199 = 17377902756647509 * 46235097144973199564251065756966919577339221 and these two factors are prime.
MATHEMATICA
Select[Range[1000], PrimeOmega[2^# - #]==2 &] (* Vincenzo Librandi, Dec 19 2014 *)
PROG
(PARI) for( i=1, 200, bigomega(2^i-i)==2 & print1(i", "))
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
M. F. Hasler, Oct 08 2009, Oct 29 2009
EXTENSIONS
More terms from Sean A. Irvine, Oct 22 2009
a(36)-a(37) from Max Alekseyev, Jun 06 2013
a(38) from Sean A. Irvine, Mar 17 2015
a(39) from Sean A. Irvine, Jun 29 2015
STATUS
approved