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 A173891 #9 Dec 08 2015 08:55:14
%S A173891 1,3,16,37,40,47,55,56,74,103,108,111,119,130,161,165,185,188,195,200,
%T A173891 219,240,272,273,292,340,359,388,420,427,465,466,509,521,554,600,606,
%U A173891 622,630,634,668,683,684,703,710,711,734,762,792,814,822,823,830,831
%N A173891 Numbers n such that the n-th noncomposite number plus the (n+2)nd noncomposite number is an even semiprime.
%C A173891 Numbers n such that (A008578(n) + A008578(n+2))/2 is prime.
%C A173891 Is this the same as A173390? - _R. J. Mathar_, Jul 22 2010
%F A173891 prime(a(n+1)-1) = n-th balanced prime.
%p A173891 A008578 := proc(n) if n = 1 then 1; else ithprime(n-1) ; end if; end proc: for n from 1 to 1000 do sp := A008578(n)+A008578(n+2) ; if type(sp,'even') and numtheory[bigomega](sp) = 2 then printf("%d,",n) ; end if; end do: # _R. J. Mathar_, Apr 25 2010
%Y A173891 Cf. A006562, A008578, A100484.
%K A173891 nonn
%O A173891 1,2
%A A173891 _Juri-Stepan Gerasimov_, Mar 01 2010
%E A173891 All but one value shifted by 1, and missing values (40, 634, 762) inserted, by _R. J. Mathar_, Apr 25 2010