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 A090530 Least multiple k of prime(n) such that (k-1,k+1) forms a twin prime pair, or 0 if no such number exists. 3
 4, 6, 30, 42, 198, 312, 102, 228, 138, 348, 1302, 1998, 1230, 1032, 282, 6360, 1062, 15738, 1608, 1278, 6132, 10428, 4482, 4272, 11058, 4242, 618, 642, 5232, 2712, 18288, 3930, 822, 1668, 1788, 11778, 3768, 5868, 5010, 9342, 23628, 3258, 17190 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) is a multiple of 6*prime(n) for n>2. Conjecture: No term is zero. LINKS Hugo Pfoertner, Table of n, a(n) for n = 1..10000 EXAMPLE a(5) = 198 = 11*18, (197,199) forms a twin prime pair. MATHEMATICA 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 *) PROG (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 CROSSREFS Cf. A014574, A090531, A294731 [a(n)/(6*prime(n))]. Sequence in context: A364737 A056221 A046849 * A154667 A093121 A248048 Adjacent sequences: A090527 A090528 A090529 * A090531 A090532 A090533 KEYWORD nonn AUTHOR Amarnath Murthy, Dec 07 2003 EXTENSIONS More terms from David Wasserman, Dec 21 2005 More terms from Stefan Steinerberger, Feb 17 2006 STATUS approved

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Last modified March 2 23:50 EST 2024. Contains 370499 sequences. (Running on oeis4.)