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 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. 4
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE 31261 is a term because 31261 = 43*727, 2*31261 - 1 = 62521 = 103*607, ..., 256*31261 - 1 = 8002561 = 7*1143223, ... 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 CROSSREFS Cf. A006881, A177210, A177211, A177212, A177213, A177214, A177215, A177216. Sequence in context: A345576 A345832 A236891 * A274045 A277171 A258577 Adjacent sequences:  A177214 A177215 A177216 * A177218 A177219 A177220 KEYWORD nonn AUTHOR Vladimir Joseph Stephan Orlovsky, May 04 2010 STATUS approved

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Last modified December 6 20:22 EST 2021. Contains 349567 sequences. (Running on oeis4.)