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 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. 7
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS 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

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Last modified December 9 04:45 EST 2021. Contains 349626 sequences. (Running on oeis4.)