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A120223

a(n) is the minimal number k>1 such that n+k and n*k+1 are primes.

+0
6

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; listen)

	OFFSET	`1,1`
	COMMENT	`If n+1 is prime then a(n)>A085063(n); if n+1 is not prime then a(n)=A085063(n).`
	EXAMPLE	`a(3)=2 because 3+2=5 and 32+1=7 are prime;` `a(8)=5 because 8+5=13 and 85+1=41 are prime,`
	MATHEMATICA	`Reap[Do[Do[If[PrimeQ[{n+x, n*x+1}]=={True, True}, Sow[x]; Break[]], {x, 2, 100}], {n, 120}]][[2, 1]]`
	CROSSREFS	`Cf. A085063, A092945, A085063, A120224, A120225.` `Sequence in context: A077199 A064652 A077600 this_sequence A065559 A087317 A086489` `Adjacent sequences: A120220 A120221 A120222 this_sequence A120224 A120225 A120226`
	KEYWORD	`nonn`
	AUTHOR	`Zak Seidov (zakseidov(AT)yahoo.com), Jun 10 2006`

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Last modified August 19 23:53 EDT 2008. Contains 142930 sequences.

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