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A177222 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. 1
38, 46, 106, 129, 133, 145, 201, 203, 235, 291, 298, 334, 335, 381, 407, 417, 458, 489, 497, 538, 579, 583, 597, 623, 626, 649, 685, 689, 694, 707, 758, 767, 781, 815, 898, 899, 921, 926, 959, 995, 1073, 1079, 1082, 1094, 1099, 1139, 1142, 1157, 1214, 1226 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

38 is a term because 38 = 2*19, 2*38 + 1 = 77 = 7*11, and 4*38 + 1 = 155 = 5*31.

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, 1000}]; lst

CROSSREFS

Cf. A006881, A111153, A177210, A177211, A177212, A177213, A177214, A177215, A177216, A177217, A177220, A177221.

Cf. A133123 (allows squares also).

Sequence in context: A078550 A295491 A133123 * A078539 A282813 A125970

Adjacent sequences:  A177219 A177220 A177221 * A177223 A177224 A177225

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, May 05 2010

STATUS

approved

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Last modified June 22 04:06 EDT 2021. Contains 345367 sequences. (Running on oeis4.)