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%I #16 Nov 13 2017 07:38:37
%S 4,6,30,42,198,312,102,228,138,348,1302,1998,1230,1032,282,6360,1062,
%T 15738,1608,1278,6132,10428,4482,4272,11058,4242,618,642,5232,2712,
%U 18288,3930,822,1668,1788,11778,3768,5868,5010,9342,23628,3258,17190
%N Least multiple k of prime(n) such that (k-1,k+1) forms a twin prime pair, or 0 if no such number exists.
%C a(n) is a multiple of 6*prime(n) for n>2. Conjecture: No term is zero.
%H Hugo Pfoertner, <a href="/A090530/b090530.txt">Table of n, a(n) for n = 1..10000</a>
%e a(5) = 198 = 11*18, (197,199) forms a twin prime pair.
%t For[n = 1, n < 40, n++, a := Prime[n]; k := 2; While[Not[PrimeQ[k*a + 1] && PrimeQ[k*a - 1]], k += 2]; Print[k*a]] (* _Stefan Steinerberger_, Feb 17 2006 *)
%o (PARI) a(n) = { my(k = 2, p = prime(n)); while (! (isprime(k*p-1) && isprime(k*p+1)), k++); k*p;} \\ _Michel Marcus_, Nov 12 2017
%Y Cf. A014574, A090531, A294731 [a(n)/(6*prime(n))].
%K nonn
%O 1,1
%A _Amarnath Murthy_, Dec 07 2003
%E More terms from _David Wasserman_, Dec 21 2005
%E More terms from _Stefan Steinerberger_, Feb 17 2006
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