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 A169643 #19 Jul 06 2025 21:39:01
%S A169643 1,2,6,10,19,28,42,51,75,79,104,114,138,148,152,178,187,212,221,247,
%T A169643 278,338,348,372,423,465,490,504,525,539,669,679,683,709,729,848,858,
%U A169643 873,883,909,961,1028,1071,1080,1089,1104,1202,1221,1247,1251,1354,1363
%N A169643 Numbers k such that neither composite(k)+-1 is composite.
%C A169643 a(n) = A066246(A014574(n)). - _Reinhard Zumkeller_, Apr 06 2010
%H A169643 Robert Israel, <a href="/A169643/b169643.txt">Table of n, a(n) for n = 1..10000</a>
%e A169643 a(1)=1 because composite(1)-1=3=prime and composite(1)+1=5=prime.
%p A169643 Comp:= remove(isprime,[$4..2000]): nC:= nops(Comp):
%p A169643 select(t -> isprime(Comp[t]-1) and isprime(Comp[t]+1), [$1..nC]); # _Robert Israel_, Oct 21 2024
%t A169643 Position[Select[Range[2000],CompositeQ],_?(AllTrue[#+{1,-1},PrimeQ]&),1,Heads->False]// Flatten (* _Harvey P. Dale_, Jan 16 2024 *)
%Y A169643 Cf. A002808, A014574, A066246.
%K A169643 nonn
%O A169643 1,2
%A A169643 _Juri-Stepan Gerasimov_, Apr 04 2010
%E A169643 Corrected by _Ray Chandler_, Apr 05 2010