A241764 Semiprimes sp such that sp-3 is also semiprime.

9, 25, 38, 49, 58, 65, 77, 85, 94, 118, 121, 122, 145, 146, 158, 161, 169, 205, 206, 209, 217, 218, 221, 262, 265, 298, 301, 302, 305, 326, 329, 358, 361, 365, 394, 398, 454, 469, 481, 485, 505, 514, 517, 529, 538, 545, 554, 562, 565, 586, 589, 614

Offset: 1

Author

K. D. Bajpai, Apr 29 2014

Keywords

• nonn

Comments

Also semiprimes of the form 2^x - x.

The primes of the form 2^x - x are in A081296.

Examples

			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.
		

Links

• K. D. Bajpai, Table of n, a(n) for n = 1..1100

Crossrefs

Cf. A001358, A092207, A123017, A198327.

Programs

Maple

with(numtheory): A241764:= proc(); if bigomega(x)=2 and bigomega(x-3)=2 then RETURN (x); fi; end: seq(A241764 (), x=1..2000);

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 *)

PARI

for(k=1, 500, if(bigomega(k)==2 && bigomega(k-3)==2, print1(k, ", "))) \\ Colin Barker, May 07 2014