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 A103557 Least k such that k*((prime(n)#)^2)-1 and k*((prime(n)#)^2)+1 are twin primes. 1
 1, 2, 7, 6, 6, 104, 152, 116, 181, 6, 78, 89, 85, 262, 133, 57, 77, 35, 237, 140, 315, 397, 663, 48, 1135, 382, 318, 261, 542, 352, 120, 31, 1430, 553, 43, 913, 1235, 122, 1008, 602, 222, 1562, 255, 6293, 1231, 2507, 1029, 1413, 5986, 3860, 45, 2622, 3033, 457 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE 1*((2*3)^2)-1 = 35 is composite, 2*((2*3)^2)-1 = 71 is prime, 2*((2*3)^2)+1 = 73 is prime twin of 71 so a(2) = 2. MATHEMATICA a[n_] := Module[{k = 1, p = Product[Prime[i], {i, 1, n}]}, While[!(PrimeQ[k*p^2-1] && NextPrime[k*p^2-1] == k*p^2+1), k++]; k]; Array[a, 50] (* Amiram Eldar, Jul 17 2021 *) CROSSREFS Cf. A001097, A002110. Sequence in context: A127817 A199173 A047232 * A210963 A210965 A189959 Adjacent sequences: A103554 A103555 A103556 * A103558 A103559 A103560 KEYWORD nonn AUTHOR Pierre CAMI, Mar 23 2005 EXTENSIONS More terms from Amiram Eldar, Jul 17 2021 STATUS approved

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Last modified January 27 02:41 EST 2023. Contains 359836 sequences. (Running on oeis4.)