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 A087030 #14 Oct 06 2013 02:53:59
%S A087030 3,4,7,6,9,8,15,14,13,12,15,14,21,20,19,18,21,20,27,26,25,24,35,34,33,
%T A087030 32,31,30,33,32,43,42,41,40,39,38,45,44,43,42,45,44,51,50,49,48,59,58,
%U A087030 57,56,55,54,65,64,63,62,61,60,63,62,73,72,71,70,69,68,75,74,73,72,75
%N A087030 n "reflected" in the next prime: a(n)=2p-n, p is smallest prime > n.
%C A087030 Take any n, find the distance from n to p: d=p-n, where p is the smallest prime > n ("next prime"), then a(n) is the number which is at the same distance from p as n, a(n)=p+d. n such that p+d=2p-n is prime in A087031.
%H A087030 Vincenzo Librandi, <a href="/A087030/b087030.txt">Table of n, a(n) for n = 1..1000</a>
%F A087030 a(n)=2p-n, p is the smallest prime > n.
%e A087030 a(2)=4 because smallest prime >2 is 3 and 2*3-2=4.
%t A087030 Table[2NextPrime[n]-n,{n,80}] (* _Harvey P. Dale_, Jun 29 2011 *)
%o A087030 (PARI) a(n)=2*nextprime(n+1)-n \\ _Charles R Greathouse IV_, Oct 03 2013
%Y A087030 Cf. A087031.
%K A087030 easy,nonn
%O A087030 1,1
%A A087030 _Zak Seidov_, Jul 31 2003