OFFSET
1,1
COMMENTS
Also semiprimes of the form 2^x - x.
The primes of the form 2^x - x are in A081296.
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..1100
EXAMPLE
a(3)= 38 = 2*19, which is semiprime: 38-3 = 35 = 5*7 is also semiprime.
a(5)= 58 = 2*29, which is semiprime: 58-3 = 55 = 5*11 is also semiprime.
MAPLE
MATHEMATICA
Flatten[Position[Partition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 700}], 4, 1], _?(First[ #] ==Last[#]==1&), {1}, Heads->False]]+3 (* Harvey P. Dale, Dec 21 2015 *)
PROG
(PARI) for(k=1, 500, if(bigomega(k)==2 && bigomega(k-3)==2, print1(k, ", "))) \\ Colin Barker, May 07 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
K. D. Bajpai, Apr 29 2014
STATUS
approved