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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
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<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [2..150] | IsSemiprime(s) where s is 4*n + 1]; // Vincenzo Librandi, Sep 22 2012
CROSSREFS
Sequence in context: A272600 A359161 A327862 * A368696 A369661 A340482
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.)