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Search: id:A109945
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| A109945 |
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Primes p such that [p,p+2] is a pair of twin primes and (p*(p+2)-1)/2 is prime. |
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1
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| 3, 5, 11, 29, 41, 71, 137, 281, 461, 599, 641, 827, 881, 1091, 1301, 1607, 2129, 2267, 2381, 2687, 3527, 3557, 3581, 4127, 4229, 4337, 4547, 5009, 5741, 6131, 6791, 6959, 7211, 7487, 7547, 8009, 8597, 8861, 9041, 9281, 10007, 10037, 10427, 10889, 11117
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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a(1)=3 because [3,5] is a pair of twin primes and (3*5-1)/2=7 is prime.
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MATHEMATICA
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lst={}; d=2; Do[p1=Prime[n]; p2=Prime[n+1]; If[p2-p1==2&&PrimeQ[(p1*p2-1)/2], AppendTo[lst, p1]], {n, 10^3}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Aug 08 2008]
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CROSSREFS
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Cf. A086870 [corresponding primes], A093706 [primes p such that (p*nextprime(p)-1)/2 is prime], A061351 [number separating twin pair is square-free].
Sequence in context: A032364 A088357 A093706 this_sequence A045536 A019338 A046134
Adjacent sequences: A109942 A109943 A109944 this_sequence A109946 A109947 A109948
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KEYWORD
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nonn
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AUTHOR
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Hugo Pfoertner (hugo(AT)pfoertner.org), Jul 09 2005
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