A177214 Numbers k that are the products of two distinct primes such that 2*k-1, 4*k-3, 8*k-7, 16*k-15 and 32*k-31 are also products of two distinct primes.

634, 694, 1387, 1942, 3403, 4714, 5062, 5269, 5353, 5617, 6805, 7495, 8587, 9427, 9847, 10018, 10123, 10705, 10942, 11293, 12139, 13162, 13798, 14191, 14989, 15406, 17197, 19735, 20866, 21439, 22114, 22585, 24277, 25009, 25351, 25399, 26734

Offset

1,1

Links

Table of n, a(n) for n=1..37.

Example

634 is a term since 634 = 2*317, 2*634 - 1 = 1267 = 7*181, 4*634 - 3 = 2533 = 17*149, 8*634 - 7 = 5065 = 5*1013, 16*634 = 10129 = 7*1447, and 32*634 = 20257 = 47*431.

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], AppendTo[lst, n]], {n, 0, 9!}]; lst

Crossrefs

Cf. A006881, A177210, A177211, A177212, A177213.

Sequence in context: A185483 A074762 A177684 * A252124 A112137 A260244

Adjacent sequences: A177211 A177212 A177213 * A177215 A177216 A177217

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, May 04 2010

Status

approved