A177210 Numbers k that are the products of two distinct primes such that 2*k-1 are also products of two distinct primes.

26, 33, 35, 39, 46, 58, 62, 65, 93, 94, 111, 118, 119, 133, 134, 146, 155, 161, 178, 183, 202, 206, 209, 214, 219, 226, 235, 237, 247, 249, 253, 259, 267, 287, 291, 295, 299, 334, 335, 341, 362, 377, 382, 386, 391, 393, 395, 407, 422, 445, 447, 451, 453, 478

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, May 04 2010

Keywords

• nonn

Examples

			26 is a term because 26 = 2*13 and 2*26 - 1 = 51 = 3*17;
33 is a term because 33 = 3*11 and 2*33 - 1 = 65 = 5*13.
		

Crossrefs

Cf. A006881.

Programs

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1,1}; lst={};Do[If[f[n]&&f[2*n-1],AppendTo[lst,n]],{n,0,4*6!}];lst
Select[Range[500],PrimeNu[#]==PrimeOmega[#]==PrimeNu[2#-1] == PrimeOmega[ 2#-1] == 2&] (* Harvey P. Dale, May 23 2014 *)