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 A305977 #6 Jun 16 2018 18:31:13
%S A305977 1,2,2,3,4,5,2,6,3,5,7,8,4,9,5,10,7,11,2,11,5,5,12,13,14,15,16,11,7,
%T A305977 17,2,18,15,5,15,19,2,20,15,13,21,17,7,11,8,15,7,22,3,23,5,8,24,13,5,
%U A305977 25,5,15,12,26,4,15,27,28,15,17,7,29,5,17,7,30,7,20,8,8,20,31,2,22,32,5,24,33,34,20,5,35,7,33,5,11,15,15,36,37,2,38,8,19,7,31
%N A305977 Filter sequence combining prime signatures of n and 2n-1.
%C A305977 Restricted growth sequence transform of A286257.
%H A305977 Antti Karttunen, <a href="/A305977/b305977.txt">Table of n, a(n) for n = 1..65537</a>
%o A305977 (PARI)
%o A305977 up_to = 65537;
%o A305977 rgs_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), u=1); for(i=1, length(invec), if(mapisdefined(om,invec[i]), my(pp = mapget(om, invec[i])); outvec[i] = outvec[pp] , mapput(om,invec[i],i); outvec[i] = u; u++ )); outvec; };
%o A305977 A046523(n) = { my(f=vecsort(factor(n)[, 2], , 4), p); prod(i=1, #f, (p=nextprime(p+1))^f[i]); }; \\ From A046523
%o A305977 Aux305977(n) = [A046523(n),A046523(n+n-1)];
%o A305977 v305977 = rgs_transform(vector(up_to,n,Aux305977(n)));
%o A305977 A305977(n) = v305977[n];
%Y A305977 Cf. A046523, A101296, A286257, A305973, A305978.
%K A305977 nonn
%O A305977 1,2
%A A305977 _Antti Karttunen_, Jun 15 2018