This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A090530 #20 Aug 25 2025 09:21:18
%S A090530 4,6,30,42,198,312,102,228,138,348,1302,1998,1230,1032,282,6360,1062,
%T A090530 15738,1608,1278,6132,10428,4482,4272,11058,4242,618,642,5232,2712,
%U A090530 18288,3930,822,1668,1788,11778,3768,5868,5010,9342,23628,3258,17190
%N 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.
%C A090530 a(n) is a multiple of 6*prime(n) for n>2. Conjecture: No term is zero.
%H A090530 Hugo Pfoertner, <a href="/A090530/b090530.txt">Table of n, a(n) for n = 1..10000</a>
%F A090530 a(n) = prime(n) * A071407(n). - _Amiram Eldar_, Aug 25 2025
%e A090530 a(5) = 198 = 11*18, (197,199) forms a twin prime pair.
%t A090530 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 A090530 (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 A090530 Cf. A014574, A071407, A090531, A294731 [a(n)/(6*prime(n))].
%K A090530 nonn,changed
%O A090530 1,1
%A A090530 _Amarnath Murthy_, Dec 07 2003
%E A090530 More terms from _David Wasserman_, Dec 21 2005
%E A090530 More terms from _Stefan Steinerberger_, Feb 17 2006