A071407 - OEIS

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A071407

Least k such that k*prime(n) + 1 and k*prime(n) - 1 are twin primes.

2, 2, 6, 6, 18, 24, 6, 12, 6, 12, 42, 54, 30, 24, 6, 120, 18, 258, 24, 18, 84, 132, 54, 48, 114, 42, 6, 6, 48, 24, 144, 30, 6, 12, 12, 78, 24, 36, 30, 54, 132, 18, 90, 36, 66, 18, 42, 30, 120, 30, 36, 42, 18, 18, 54, 84, 60, 12, 210, 12, 6, 60, 150, 102, 6, 210, 30, 24, 6

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OFFSET

1,1

COMMENTS

Note that 6 divides a(n) for n > 2. - T. D. Noe, Jan 07 2013

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

EXAMPLE

n=4: prime(4)=7, a(4)=6 because 6*prime(4)=42 and {41,43} are primes.

MATHEMATICA

Table[fl=1; Do[s=(Prime[j])*k; If[PrimeQ[s-1]&&PrimeQ[s+1]&&Equal[fl, 1], Print[{j, k}]; fl=0], {k, 1, 2*j^2}], {j, 0, 100}]

PROG