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Search: id:A137479
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| A137479 |
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Greatest common divisor of (the average of the n-1st twin prime pair) and (the average of the nth twin prime pair). |
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+0
1
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| 2, 6, 6, 6, 6, 6, 12, 6, 6, 6, 6, 30, 12, 6, 6, 12, 30, 6, 6, 12, 12, 12, 6, 6, 6, 30, 6, 6, 6, 30, 6, 6, 6, 6, 6, 12, 6, 6, 6, 12, 6, 6, 6, 6, 6, 12, 12, 6, 6, 24, 12, 12, 6, 6, 6, 12, 6, 6, 6, 6, 6, 6, 6, 24, 6, 6, 6, 6, 42, 30, 6, 6, 6, 6, 6, 24, 6, 30, 6, 6, 30, 120, 48, 12, 6, 6, 30, 30, 12, 6
(list; graph; listen)
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OFFSET
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1,1
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FORMULA
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a(n)=gcd( A014574(n-1),A014574(n)). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 05 2008
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EXAMPLE
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Average of twin prime pairs:4,6,12,18,30,42,60,72,102
GCD[4, 6] = 2
GCD[12, 6] = 6
GCD[12, 18] = 6
GCD[30, 18] = 6
GCD[30, 42] = 6
GCD[60, 42] = 6
GCD[60, 72] = 12
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MAPLE
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A014574 := proc(n) local p ; if n = 0 then 4 ; else p := nextprime( A014574(n-1) ) ; while not isprime(p+2) do p := nextprime(p) ; od ; RETURN( p+1) ; fi ; end: A137479 := proc(n) igcd( A014574(n-1), A014574(n)) ; end: seq(A137479(n), n=1..130) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 05 2008
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MATHEMATICA
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GCD[a = Select[Range[5, 998], PrimeQ[ # - 1] && PrimeQ[ # + 1] &], b = Select[Range[4, 881], PrimeQ[ # - 1] && PrimeQ[ # + 1] &]]
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CROSSREFS
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Sequence in context: A141624 A134413 A134201 this_sequence A048765 A103643 A079892
Adjacent sequences: A137476 A137477 A137478 this_sequence A137480 A137481 A137482
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KEYWORD
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nonn,uned
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AUTHOR
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Vladimir Orlovsky (4vladimir(AT)gmail.com), Apr 22 2008
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 05 2008
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