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 A290704 #12 Aug 25 2017 16:40:41 %S A290704 1680,4200,27000,175392,282960,707400,1668480,3344544,5658480, %T A290704 14146200,48644064,90008880,130110624,225022200,357994728,460763160, %U A290704 607281696,1926458352,3830537880,5857651296,7840881216,8414628480,8704032876,8843224500,14279194512,29522053080 %N A290704 Solutions to 2*x - phi(x) = sigma(x)/2, where phi(x) is the Euler totient function of x. %D A290704 Like A099650 but with totient phi(x) replaced by cototient x - phi(x). %e A290704 phi(1680) = 384, sigma(1680) = 5952 and 2*1680 - 384 = 2976 = 5952/2. %p A290704 with(numtheory): P:=proc(q) local n; for n from 1 to q do %p A290704 if 2*n-phi(n)=sigma(n)/2 then print(n); fi; od; end: P(10^9); %Y A290704 Cf. A000010, A051953, A099650, A111592, A290703. %K A290704 nonn %O A290704 1,1 %A A290704 _Paolo P. Lava_, Aug 09 2017 %E A290704 a(10)-a(26) from _Giovanni Resta_, Aug 25 2017