A138025 Numbers that remain prime through 7 iterations of function f(x) = 2x + 1.

19099919, 52554569, 85864769, 171729539, 198479579, 226366139, 305192579, 344319029, 396959159, 474118349, 574964129, 610385159, 685066979, 764406059, 1085182229, 1126004219, 1195651139, 1372213439, 1484454269, 1573750049, 2270291519, 2365144079, 2400025739

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, May 01 2008

Keywords

• nonn

Comments

n, 2*n+1, 4*n+3, 8*n+7, 16*n+15, 32*n+31, 64*n+63, and 128*n+127 are primes. - John Cerkan, Dec 04 2016

Programs

Mathematica

Select[Prime[Range[10^7]],PrimeQ[a1=2*#+1]&&PrimeQ[a2=2*a1+1]&&PrimeQ[a3=2*a2+1]&&PrimeQ[a4=2*a3+1]&&PrimeQ[a5=2*a4+1]&&PrimeQ[a6=2*a5+1]&&PrimeQ[a7=2*a6+1] &]

Formula

a(n) == 29 (mod 30). - John Cerkan, Nov 30 2016

Extensions

More terms from Vladimir Joseph Stephan Orlovsky, Jan 17 2009

a(7)-a(23) from John Cerkan, Nov 30 2016