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Search: id:A087383
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| A087383 |
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Numbers n such that prime(prime(n)) and n are twin primes. |
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+0
1
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| 3, 5, 7, 13, 29, 41, 43, 59, 71, 103, 107, 137, 149, 193, 199, 271, 281, 311, 347, 349, 433, 463, 569, 617, 619, 811, 827, 857, 859, 881, 1031, 1153, 1229, 1289, 1481, 1607, 1699, 1723, 1933, 1949, 1951, 1997, 2113, 2551, 2593, 2657, 3001, 3257, 3373, 3463
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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The 29th prime is 109 and prime(109) is 599 paired with the prime 601.
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MATHEMATICA
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TwinPrimeQ[n_]:=If[PrimeQ[n], If[PrimeQ[n-2]||PrimeQ[n+2], True, False], False](*TwinPrimeQ*) lst={}; Do[If[TwinPrimeQ[Prime[Prime[n]]]&&TwinPrimeQ[n], AppendTo[lst, n]], {n, 7!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Sep 07 2008]
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PROGRAM
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(PARI) twips(n) = { c1=0; c2=0; forprime(x=3, n, if(isprime(x+2), c1++); x1=prime(prime(x)); if(isprime(x-2) || isprime(x+2), if(isprime(x1-2) || isprime(x1+2), print1(x", "); c2++; ) ) ); print(); print(c2/c1+.0) }
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CROSSREFS
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Adjacent sequences: A087380 A087381 A087382 this_sequence A087384 A087385 A087386
Sequence in context: A024946 A096177 A128547 this_sequence A038928 A089740 A047933
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Oct 21 2003
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