login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A070418 Numbers k such that k and phi(k) have the same number of divisors. 4
1, 3, 14, 15, 22, 28, 44, 46, 50, 56, 68, 70, 78, 88, 92, 94, 110, 112, 118, 166, 174, 176, 184, 188, 198, 214, 224, 228, 230, 234, 236, 255, 260, 294, 306, 318, 332, 334, 342, 352, 358, 368, 376, 414, 428, 448, 454, 462, 470, 472, 492, 500, 526, 550, 580, 590 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
This is an infinite sequence; for example, 2^(m-1)*5^m is in the sequence for all m >= 2. See Bellaouar et al. 2023. - Allen Stenger, Feb 16 2024
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..8407 (for values up to 500000)
Djamel Bellaouar, Abdelmadjid Boudaoud and Rafael Jakimczuk, Notes on the equation d(n) = d(phi(n)) and related inequalities, Math. Slovaca 73 (2023), no. 3, 613-632.
MATHEMATICA
Select[Range[600], DivisorSigma[0, #]==DivisorSigma[0, EulerPhi[#]]&] (* Harvey P. Dale, Sep 04 2015 *)
PROG
(PARI) for(n=1, 900, if(numdiv(n)==numdiv(eulerphi(n)), print1(n, ", ")))
CROSSREFS
Cf. A000005, A000010 (phi), A116518 (odd terms).
Sequence in context: A171653 A055435 A242868 * A178363 A294997 A354740
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 12 2002
STATUS
approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 23 06:04 EDT 2024. Contains 371906 sequences. (Running on oeis4.)