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A120223
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a(n) is the minimal number k>1 such that n+k and n*k+1 are primes.
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5
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2, 3, 2, 3, 2, 5, 4, 5, 2, 3, 2, 5, 4, 3, 2, 7, 6, 11, 10, 3, 2, 9, 6, 13, 4, 3, 4, 15, 2, 7, 10, 11, 10, 3, 2, 5, 4, 5, 2, 7, 2, 5, 4, 9, 14, 13, 6, 5, 4, 3, 2, 21, 14, 5, 6, 5, 4, 9, 12, 7, 6, 5, 10, 3, 2, 5, 4, 15, 2, 3, 8, 25, 6, 27, 8, 3, 6, 11, 4, 3, 2, 15, 6, 5, 12, 11, 20, 15, 12, 7, 6, 5, 4, 3
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| If n+1 is prime then a(n)>A085063(n); if n+1 is not prime then a(n)=A085063(n).
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EXAMPLE
| 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
| Reap[Do[Do[If[PrimeQ[{n+x, n*x+1}]=={True, True}, Sow[x]; Break[]], {x, 2, 100}], {n, 120}]][[2, 1]]
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CROSSREFS
| Cf. A085063, A092945, A085063, A120224, A120225.
Sequence in context: A204895 A064652 A077600 * A065559 A087317 A086489
Adjacent sequences: A120220 A120221 A120222 * A120224 A120225 A120226
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KEYWORD
| nonn
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Jun 10 2006
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