A177217 The products k of two distinct primes such that 2*k-1, 4*k-3, 8*k-7, 16*k-15, 32*k-31, 64*k-63, 128*k-127 and 256*k-255 are also products of two distinct primes.

31261, 36199, 44869, 49471, 62521, 72397, 83086, 138994, 173311, 182527, 224962, 259891, 277987, 346621, 370126, 415423, 443746, 464245, 480331, 519781, 544006, 563326, 599245, 693241, 784681, 880561, 928489, 980743, 991237, 1032937

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, May 04 2010

Keywords

• nonn

Examples

			31261 is a term because 31261 = 43*727, 2*31261 - 1 = 62521 = 103*607, ..., 256*31261 - 1 = 8002561 = 7*1143223, ...
		

Crossrefs

Cf. A006881, A177210, A177211, A177212, A177213, A177214, A177215, A177216.

Programs

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1,1}; lst={};Do[If[f[n]&&f[2*n-1]&&f[4*n-3]&&f[8*n-7]&&f[16*n-15]&&f[32*n-31]&&f[64*n-63]&&f[128*n-127]&&f[256*n-255],AppendTo[lst,n]],{n,31261,5*9!}];lst