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 A177983 #10 Nov 08 2022 17:01:05
%S A177983 3,5,4,9,8,7,15,11,10,21,4,13,17,17,16,18,20,4,39,23,22,45,5,25,30,4,
%T A177983 28,32,32,31,33,35,4,69,38,37,40,41,5,81,4,43,47,5,46,6,50,4,99,53,52,
%U A177983 105,56,55,111,4,58,6,7,5,8,65,4,129,5,67,72,71,70,75,4,7,77,77,76,78,80,4,82,83
%N A177983 a(1)=3. Otherwise the average of the least prime divisors of 2n-1 and 2n+3.
%C A177983 Lim inf (n->infinity) (a(n)/n)=0.
%C A177983 If there exist infinitely many cousin primes (A023200), then lim sup (n->infinity) (a(n)/ n)=2.
%F A177983 a(n) = (A090368(n)+A090368(n+2))/2 . [_R. J. Mathar_, Oct 25 2010]
%p A177983 A090368 := proc(n) A020639(2*n-1) ; end proc:
%p A177983 A177983 := proc(n) (A090368(n)+A090368(n+2)) /2 ; end proc:
%p A177983 seq(A177983(n),n=1..80) ; # _R. J. Mathar_, Oct 25 2010
%t A177983 Table[Mean[{FactorInteger[2n-1][[1,1]],FactorInteger[2n+3][[1,1]]}],{n,80}] (* _Harvey P. Dale_, Nov 08 2022 *)
%o A177983 (PARI) a(n) = if (n==1, 3, (factor(2*n-1)[1,1] + factor(2*n+3)[1,1])/2); \\ _Michel Marcus_, Feb 08 2016
%Y A177983 Cf. A020639, A177961.
%K A177983 nonn,easy
%O A177983 1,1
%A A177983 _Vladimir Shevelev_, May 16 2010
%E A177983 I corrected a(25). It should be 30 (not 31) _Vladimir Shevelev_, May 22 2010
%E A177983 More terms from _R. J. Mathar_, Oct 25 2010