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 A167427 #8 Feb 18 2019 11:11:38 %S A167427 1,1,1,10,10,16,16,28,28,40,40,58,58,70,70,100,100,106,106,136,136, %T A167427 148,148,178,178,190,190,196,196,226,226,238,238,268,268,280,280,310, %U A167427 310,346,346,418,418,430,430,460,460,520,520,568,568,598,598,616,616,640 %N A167427 Largest non-isolated nonprime < n-th non-isolated (or twin) prime. %e A167427 a(1)=1 (<3); a(2)=1 (<5); a(3)=1 (<7); a(4)=10 (<11). %p A167427 isA164276 := proc(n) not isprime(n) and ( not isprime(n+1) or not isprime(n-1) ) ; end proc: %p A167427 isA001097 := proc(n) isprime(n) and ( isprime(n+2) or isprime(n-2) ); end proc: %p A167427 A001097 := proc(n) option remember; if n =1 then 3; else for a from procname(n-1)+2 by 2 do if isA001097(a) then return a; end if; end do: end if; end proc: %p A167427 A167427 := proc(n) for a from A001097(n)-1 by -1 do if isA164276(a) then return a; end if; end do: end proc: %p A167427 seq(A167427(n),n=1..120) ; # _R. J. Mathar_, May 30 2010 %Y A167427 Cf. A001097, A164276. %K A167427 nonn %O A167427 1,4 %A A167427 _Juri-Stepan Gerasimov_, Nov 03 2009 %E A167427 Entries checked by _R. J. Mathar_, May 30 2010