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A190299 Squarefree semiprimes of the form 4k+1. 2
21, 33, 57, 65, 69, 77, 85, 93, 129, 133, 141, 145, 161, 177, 185, 201, 205, 209, 213, 217, 221, 237, 249, 253, 265, 301, 305, 309, 321, 329, 341, 365, 377, 381, 393, 413, 417, 437, 445, 453, 469, 473, 481, 485, 489, 493, 497, 501, 505, 517, 533, 537, 545 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

There are 961 squarefree semiprimes of the form 4k+1 below 10000.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Semiprime

Wikipedia, Semiprime

MATHEMATICA

Select[Range[1, 600, 4], Last/@FactorInteger[#]=={1, 1}&]

CROSSREFS

Cf. A001358, A006881, A080774.  Union of A131574 and A016105.

Sequence in context: A176945 A070006 A189986 * A280262 A084109 A016105

Adjacent sequences:  A190296 A190297 A190298 * A190300 A190301 A190302

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, May 07 2011

EXTENSIONS

Edited by Ray Chandler, Dec 16 2011

STATUS

approved

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Last modified November 13 10:29 EST 2019. Contains 329093 sequences. (Running on oeis4.)