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 A108181 Semiprimes of the form 4n + 1. 8
 9, 21, 25, 33, 49, 57, 65, 69, 77, 85, 93, 121, 129, 133, 141, 145, 161, 169, 177, 185, 201, 205, 209, 213, 217, 221, 237, 249, 253, 265, 289, 301, 305, 309, 321, 329, 341, 361, 365, 377, 381, 393, 413, 417, 437, 445, 453, 469, 473, 481, 485, 489, 493, 497 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Either a(n)=(4*i+1)*(4*j+1) or a(n)=(4*i+3)*(4*j+3); - Reinhard Zumkeller, Jun 15 2005 A107978 is a subsequence. - Reinhard Zumkeller, Jun 15 2005 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 K. Ford, Jason Sneed, Chebyshev's Bias for products of two primes, Exper. Math. 19 (4) (2010) 385-398 MATHEMATICA Select[4Range[0, 150] + 1, PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 22 2012 *) PROG (Magma) IsSemiprime:= func; [s: n in [2..150] | IsSemiprime(s) where s is 4*n + 1]; // Vincenzo Librandi, Sep 22 2012 CROSSREFS Cf. A080774, A001358, A002144, A002145, A107978, A121387. Sequence in context: A272600 A359161 A327862 * A368696 A369661 A340482 Adjacent sequences: A108178 A108179 A108180 * A108182 A108183 A108184 KEYWORD easy,nonn AUTHOR Giovanni Teofilatto, Jun 14 2005 EXTENSIONS Corrected and extended by Reinhard Zumkeller, Jun 15 2005 STATUS approved

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Last modified April 20 03:03 EDT 2024. Contains 371798 sequences. (Running on oeis4.)