This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A015704 a(n) is the smallest number m such that phi(m) + sigma(m) = n*m. 4
 1, 312, 23760 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS 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 a(5) >= 2*10^9. - Farideh Firoozbakht, Jan 22 2008 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 LINKS Richard K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360. PROG (PARI) a(n) = my(m = 1); while(sigma(m)+eulerphi(m) != n*m, m++); m; \\ Michel Marcus, Oct 04 2017 CROSSREFS Cf. A011251, A011254. Sequence in context: A156403 A296527 A107508 * A156406 A283492 A112729 Adjacent sequences:  A015701 A015702 A015703 * A015705 A015706 A015707 KEYWORD nonn,bref,more AUTHOR EXTENSIONS Name, offset and data corrected by Farideh Firoozbakht, Jan 22 2008 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 16 13:16 EDT 2019. Contains 324152 sequences. (Running on oeis4.)