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 A064213 #8 Jun 24 2018 18:30:29
%S A064213 4,2,2,4,10,40,58,64,28,24,8,210,70,36,12,4,78,26,28,20,90,30,10,630,
%T A064213 210,70,82,416,612,204,68,930,310,406,1078,1164,388,176,190,334,190,
%U A064213 726,242,1004,398,1430,1372,2730,910,1560,520
%N A064213 Least k such that k*3^n +- 1 are twin primes.
%C A064213 k must be even because 3^n is odd. - _Harry J. Smith_, Sep 10 2009
%H A064213 Harry J. Smith, <a href="/A064213/b064213.txt">Table of n, a(n) for n = 0..225</a>
%t A064213 Do[ k = 1; While[ ! PrimeQ[ k*3^n + 1 ] || ! PrimeQ[ k*3^n - 1 ], k++ ]; Print[ k ], {n, 0, 50} ]
%o A064213 (PARI) { for (n=0, 225, k=0; p=3^n; until (isprime(k*p - 1) && isprime(k*p + 1), k+=2); write("b064213.txt", n, " ", k); ) } \\ _Harry J. Smith_, Sep 10 2009
%Y A064213 Cf. A063983.
%K A064213 nonn
%O A064213 0,1
%A A064213 _Robert G. Wilson v_, Sep 21 2001
%E A064213 Offset changed from 1 to 0 by _Harry J. Smith_, Sep 10 2009