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 A104278 #27 Feb 05 2025 21:50:16
%S A104278 13,17,25,28,32,38,43,46,47,58,59,60,61,62,67,71,72,73,77,80,85,88,92,
%T A104278 93,94,101,102,103,104,107,108,109,110,118,122,123,124,127,130,133,
%U A104278 137,143,144,145,148,149,150,151,152,160,161,162,163,164,167,170,171,172
%N A104278 Numbers m such that 2m+1 and 2m-1 are not primes.
%C A104278 Complement of A147820. - _Omar E. Pol_, Nov 17 2008
%C A104278 m is in the sequence iff A177961(m)<m. - _Vladimir Shevelev_, May 16 2010
%H A104278 Reinhard Zumkeller, <a href="/A104278/b104278.txt">Table of n, a(n) for n = 1..10000</a>
%F A104278 a(n) = (A025583-1)/2. - _Bill McEachen_, Feb 05 2025
%e A104278 a(1)=13 is the first number satisfying simultaneously the two rules.
%t A104278 Select[ Range[300], !PrimeQ[2# + 1] && !PrimeQ[2# - 1] &] (* _Robert G. Wilson v_, Apr 18 2005 *)
%t A104278 Select[Range[300],NoneTrue[2#+{1,-1},PrimeQ]&] (* The program uses the NoneTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Jul 07 2015 *)
%o A104278 (Haskell)
%o A104278 a104278 n = a104278_list !! (n-1)
%o A104278 a104278_list = [m | m <- [1..],
%o A104278 a010051' (2 * m - 1) == 0 && a010051' (2 * m + 1) == 0]
%o A104278 -- _Reinhard Zumkeller_, Aug 04 2015
%o A104278 (PARI) select( {is_A104278(n)=!isprime(2*n-1)&&!isprime(2*n+1)}, [1..222]) \\ _M. F. Hasler_, Apr 29 2024
%Y A104278 Intersection of A047845 and A104275.
%Y A104278 Cf. A040040, A147820, A025583.
%Y A104278 Cf. A010051, A002808, A099047.
%K A104278 easy,nonn
%O A104278 1,1
%A A104278 _Alexandre Wajnberg_, Apr 17 2005
%E A104278 More terms from _Robert G. Wilson v_, Apr 18 2005