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 A160218 #4 May 01 2013 21:08:57
%S A160218 2,3,14,20,32,301,1065
%N A160218 Index at which n-th prime occurs in A160256, or -1 if the prime never occurs.
%C A160218 A160256(a(n))=A000040(n) if and only if both Conjectures 1 and 2 are true:
%C A160218 Conjecture 1: Primes occur in A160256 in increasing order.
%C A160218 Conjecture 2: All primes occur in A160256.
%C A160218 Conjecture 3: Except for A160256(4)=4, the least positive integer which does not occur in A160256 up to a given index is always a prime (and thus of the form A160256(a(k)) for some k).
%C A160218 Conjecture 4: A160256(a(n)) is always the least positive integer which did not occur earlier in A160256.
%o A160218 (PARI) list_A160218(n)={ my(a1=1,a2=1,S=[]); until( isprime(a1) & !print1(#S,",") & !n--, for( a=1,9e9, a*a1%a2 & next; setsearch(S,a) & next; a2=a1; S=setunion(S,Set(a1=a)); /*print1(a",");*/ next(2)); error);vecsort(eval(S)) }
%Y A160218 Cf. A160256, A151413.
%K A160218 hard,more,nonn
%O A160218 1,1
%A A160218 _M. F. Hasler_, May 06 2009
%E A160218 Edited by _N. J. A. Sloane_, May 16 2009