A177211 Numbers k that are the products of two distinct primes such that 2*k-1 and 4*k-3 are also products of two distinct primes.

33, 118, 119, 134, 146, 226, 247, 249, 287, 295, 334, 335, 386, 391, 393, 395, 422, 478, 493, 497, 502, 519, 551, 583, 589, 614, 629, 634, 694, 697, 721, 731, 749, 755, 789, 802, 817, 843, 879, 898, 955, 958, 985, 989, 1003, 1037, 1079, 1114, 1154, 1159, 1177

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

33 is a term because 33 = 3*11, 2*33 - 1 = 65 = 5*13 and 2*65 - 1 = 4*33 - 3 = 129 = 3*43.

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1, 1}; lst={}; Do[If[f[n]&&f[2*n-1]&&f[4*n-3], AppendTo[lst, n]], {n, 0, 7!}]; lst
tdpQ[n_]:=PrimeNu[n]==PrimeOmega[n]==PrimeNu[2n-1]==PrimeOmega[2n-1] == PrimeNu[4n-3]==PrimeOmega[4n-3]==2; Select[Range[1200], tdpQ] (* Harvey P. Dale, Nov 15 2020 *)

Crossrefs

Cf. A006881, A177210

Sequence in context: A044284 A044665 A140161 * A337626 A301633 A039440

Adjacent sequences: A177208 A177209 A177210 * A177212 A177213 A177214

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, May 04 2010

Extensions

Definition clarified by Harvey P. Dale, Nov 15 2020

Status

approved