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Search: id:A085063
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| A085063 |
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a(n) is the minimal number k such that n+k and n*k+1 are primes. |
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+0
7
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| 1, 1, 2, 1, 2, 1, 4, 5, 2, 1, 2, 1, 4, 3, 2, 1, 6, 1, 10, 3, 2, 1, 6, 13, 4, 3, 4, 1, 2, 1, 10, 11, 10, 3, 2, 1, 4, 5, 2, 1, 2, 1, 4, 9, 14, 1, 6, 5, 4, 3, 2, 1, 14, 5, 6, 5, 4, 1, 12, 1, 6, 5, 10, 3, 2, 1, 4, 15, 2, 1, 8, 1, 6, 27, 8, 3, 6, 1, 4, 3, 2, 1, 6, 5, 12, 11, 20, 1, 12, 7, 6, 5, 4, 3, 2, 1, 4, 5
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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If n+1 is prime then a(n)=1; if n+1 is not prime then a(n)=A120223(n).
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EXAMPLE
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a(3)=2 because 3+2=5 and 3*2+1=7 are prime;
a(8)=5 because 8+5=13 and 8*5+1=41 are prime,
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MATHEMATICA
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Reap[Do[Do[If[PrimeQ[{n+x, n*x+1}]=={True, True}, Sow[x]; Break[]], {x, 1, 100}], {n, 120}]][[2, 1]]
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CROSSREFS
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Cf. A092945, A120223, A120224, A120225.
Sequence in context: A079499 A166235 A143591 this_sequence A058511 A131044 A106380
Adjacent sequences: A085060 A085061 A085062 this_sequence A085064 A085065 A085066
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jun 28 2003
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EXTENSIONS
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Corrected and extended by Zak Seidov (zakseidov(AT)yahoo.com), Jun 10 2006
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