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 A073666 #22 Dec 15 2017 17:35:58
%S A073666 1,2,3,4,7,6,5,8,9,12,13,10,15,14,17,18,11,30,19,22,16,21,20,23,26,33,
%T A073666 34,27,28,24,25,42,31,36,32,29,38,39,48,37,40,43,46,51,50,45,52,49,54,
%U A073666 44,47,56,41,62,59,60,53,66,35,68,57,58,55,70,61,76,63,74,69,72,71,98
%N A073666 Rearrangement of natural numbers such that a(k)*a(k+1) + 1 is a prime for all k.
%H A073666 Ivan Neretin, <a href="/A073666/b073666.txt">Table of n, a(n) for n = 1..1000</a>
%t A073666 a[1]=1; a[n_]:=a[n]=(For[c=Sort[Table[a[k], {k, n-1}]]; d=Append[c, Last[c]+1]; m=First[Complement[Range[Last[d]], c]], MemberQ[c, m]||!PrimeQ[m*a[n-1]+1], m++ ]; m); Table[a[k], {k, 70}] (* _Farideh Firoozbakht_, Apr 14 2004 *)
%o A073666 (PARI) A073666(n,show=1,a=1,u=[a])={for(n=2,n,show&&print1(a",");for(k=u[1]+1,9e9,!setsearch(u,k) && isprime(a*k+1) && (a=k) && break);u=setunion(u,[a]); while(#u>1&&u[2]==u[1]+1,u=u[2..-1]));a} \\ Use 2nd, 3rd or 4th optional arg to display intermediate terms, to use another starting value, to exclude some terms. - _M. F. Hasler_, Nov 24 2015
%Y A073666 Cf. A092842, A081942, A081943, A092829.
%Y A073666 Cf. A073667.
%Y A073666 Cf. A096100.
%K A073666 nonn
%O A073666 1,2
%A A073666 _Amarnath Murthy_, Aug 10 2002
%E A073666 More terms from _Jason Earls_, Aug 26 2002
%E A073666 Offset changed to 1 by _Ivan Neretin_, Mar 06 2016