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Search: id:A124936
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| A124936 |
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Numbers n such that n -/+ 1 are semiprimes. |
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+0
9
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| 5, 34, 50, 56, 86, 92, 94, 120, 122, 142, 144, 160, 184, 186, 202, 204, 214, 216, 218, 220, 236, 248, 266, 288, 290, 300, 302, 304, 320, 322, 328, 340, 392, 394, 412, 414, 416, 446, 452, 470, 472, 516, 518, 528, 534, 536, 544, 552, 580, 582, 590, 634, 668
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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All but first term are even. Cf. A092207 Numbers n such that n and n+2 are semiprimes, A086005 Numbers n such that n, n -/+ 1 are semiprimes, A086006 Primes p such that 2*p-1 and 2*p+1 are semiprimes, A082130 2*n-1 and 2*n+1 are semiprimes.
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LINKS
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Zak Seidov, Table of n, a(n) for n = 1..1000
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FORMULA
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a(n)=A092207(n)+1; at n>=2, a(n)=2*A082130(n-1).
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MATHEMATICA
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lst={}; Do[If[Plus@@Last/@FactorInteger[n-1]==2&&Plus@@Last/@FactorInteger[n+1]==2, AppendTo[lst, n]], {n, 7!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 01 2009]
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CROSSREFS
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Cf. A086005, A086006, A082130, A092207.
Sequence in context: A134152 A140424 A145505 this_sequence A068560 A039773 A135973
Adjacent sequences: A124933 A124934 A124935 this_sequence A124937 A124938 A124939
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Nov 13 2006
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