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Search: id:A107978
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| A107978 |
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Bigaussian semiprimes. Real Gaussian semiprimes. Products of two primes of the form 4n+3 (A002145). |
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5
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| 9, 21, 33, 49, 57, 69, 77, 93, 121, 129, 133, 141, 161, 177, 201, 209, 213, 217, 237, 249, 253, 301, 309, 321, 329, 341, 361, 381, 393, 413, 417, 437, 453, 469, 473, 489, 497, 501, 517, 529, 537, 553, 573, 581, 589, 597, 633, 649, 669, 681, 713, 717, 721, 737
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Every odd semiprime must be in one of these three disjoint sets: the product of two primes of the form 4n+1, or the product of two primes of the form 4n+3, or the product of a prime of the form 4n+1 and a prime of the form 4n+3. Products of two primes of the form 4n+3 are to be confused with Gaussian Semiprimes in the complex plane (Gaussian integers in the complex plane which are the product of exactly two Gaussian primes), which make an interesting 2-D diagram. The product of two primes of the form 4n+3 is itself of the form 4n+1.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1000
Eric Weisstein's World of Mathematics, Semiprime.
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FORMULA
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{a(n)} = {p*q: p and q both elements of A002145}.
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CROSSREFS
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Cf. A001358, A002145.
Cf. A080774, A121387 (the other two sets of odd semiprimes)
Sequence in context: A133929 A086470 A017629 this_sequence A043112 A043892 A146069
Adjacent sequences: A107975 A107976 A107977 this_sequence A107979 A107980 A107981
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Jun 12 2005
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