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A060256 Smallest multiple a(n) of n-th primorial q(n) such that a(n)*q(n)-1 and a(n)*q(n)+1 are a pair of twin primes. 9
2, 1, 1, 2, 1, 6, 8, 11, 4, 16, 22, 4, 74, 24, 37, 28, 14, 11, 242, 11, 91, 20, 83, 91, 35, 80, 48, 47, 226, 2, 12, 203, 30, 38, 356, 54, 266, 108, 305, 227, 173, 1185, 738, 13, 382, 277, 455, 433, 173, 1303, 926, 1162, 164, 298, 69, 121, 702, 1670, 36, 570, 170, 204 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Pierre CAMI, Table of n, a(n) for n = 1..500

EXAMPLE

30030*j-1 or 30030*j+1 are not both primes for j=1,2,3,4,5. But for j=6 {180179,180181} are twin primes. So a(6)=6.

MATHEMATICA

smp[n_]:=Module[{k=1}, While[!PrimeQ[k*n+1]||!PrimeQ[k*n-1], k++]; k]; Table[ smp[n], {n, FoldList[Times, Prime[Range[70]]]}] (* Harvey P. Dale, Oct 27 2016 *)

CROSSREFS

Cf. A001359, A002110, A060229-A060232, A060255, A057706.

Sequence in context: A326407 A126127 A230324 * A103899 A093324 A169676

Adjacent sequences:  A060253 A060254 A060255 * A060257 A060258 A060259

KEYWORD

nonn

AUTHOR

Labos Elemer, Mar 22 2001

EXTENSIONS

Corrected and extended by Ray Chandler, Apr 03 2009

STATUS

approved

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Last modified June 15 17:41 EDT 2021. Contains 345049 sequences. (Running on oeis4.)