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 A015704 #36 Jan 16 2024 01:57:54 %S A015704 1,312,23760,336280120525440 %N A015704 a(n) is the smallest number m such that phi(m) + sigma(m) = n*m. %C A015704 The offset is 2, because for all numbers m, phi(m)+sigma(m) >= 2*m, so there is no number a(1) such that phi(a(1))+sigma(a(1))=1*a(1). - _Farideh Firoozbakht_, Jan 22 2008 %C A015704 a(5) >= 2*10^9. - _Farideh Firoozbakht_, Jan 22 2008 %C A015704 10^13 < a(5) <= 336280120525440. _Charles R Greathouse IV_ showed that 6 divides a(5). 336280120525440 and 60493590969525342720 are the only m values I found such that phi(m) + sigma(m) = 5*m. - _Donovan Johnson_, Sep 11 2012 %H A015704 Richard K. Guy, <a href="http://www.jstor.org/stable/2974586">Divisors and desires</a>, Amer. Math. Monthly, 104 (1997), 359-360. %o A015704 (PARI) a(n) = my(m = 1); while(sigma(m)+eulerphi(m) != n*m, m++); m; \\ _Michel Marcus_, Oct 04 2017 %Y A015704 Cf. A011251, A011254. %K A015704 nonn,hard,more %O A015704 2,2 %A A015704 _Robert G. Wilson v_ %E A015704 Name, offset and data corrected by _Farideh Firoozbakht_, Jan 22 2008 %E A015704 a(5) confirmed by _Martin Ehrenstein_, Jan 15 2024