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 A305818 #7 Jun 15 2018 09:26:21
%S A305818 0,1,1,2,1,3,1,2,2,3,1,4,1,2,3,3,1,5,1,3,2,3,1,5,2,2,3,3,1,6,1,3,3,2,
%T A305818 2,6,1,2,2,5,1,6,1,3,5,3,1,5,1,3,2,3,1,6,3,4,2,3,1,8,1,2,4,3,2,6,1,2,
%U A305818 3,5,1,8,1,2,4,2,2,6,1,5,3,3,1,6,2,2,3,5,1,9,1,3,2,2,2,6,1,3,5,5,1,5,1,4,6
%N A305818 Number of proper divisors d of n such that 2d+1 is a prime.
%C A305818 Number of terms of A005097 which are less than n that divide n.
%H A305818 Antti Karttunen, <a href="/A305818/b305818.txt">Table of n, a(n) for n = 1..65537</a>
%F A305818 a(n) = Sum_{d|n, d<n} A101264(d).
%F A305818 a(n) = A086668(n) - A101264(n).
%o A305818 (PARI) A305818(n) = sumdiv(n, d, (d<n)*isprime(d+d+1));
%Y A305818 Cf. A005097, A086668, A101264.
%K A305818 nonn
%O A305818 1,4
%A A305818 _Antti Karttunen_, Jun 15 2018