login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A230203 Numbers n such that sigma(phi(n)) > n. 4
5, 7, 9, 11, 13, 17, 19, 21, 23, 25, 26, 27, 29, 31, 33, 35, 37, 38, 39, 41, 43, 45, 47, 49, 51, 52, 53, 55, 56, 57, 59, 61, 62, 63, 65, 67, 69, 71, 73, 74, 75, 76, 77, 79, 81, 82, 83, 85, 86, 87, 88, 89, 91, 93, 95, 97, 99, 101, 103, 104, 105, 107, 109, 111, 112, 113, 115, 116, 117, 119 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It seems that the odd number n isn't in the sequence if and only if n+2 is Fermat prime.

LINKS

Table of n, a(n) for n=1..70.

MAPLE

for n do if sigma(phi(n))>n then print{n} fi od:

MATHEMATICA

Select[Range[150], DivisorSigma[1, EulerPhi[#]]>#&] (* Harvey P. Dale, Apr 14 2019 *)

CROSSREFS

Cf. A230201, A001229, A018784, A066694, A000203, A000010, A227011, A227927, A062402, A230203, A018784.

Sequence in context: A005763 A035034 A065155 * A303578 A282057 A088502

Adjacent sequences:  A230200 A230201 A230202 * A230204 A230205 A230206

KEYWORD

nonn

AUTHOR

Vladimir Letsko, Oct 11 2013

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 23 01:48 EST 2020. Contains 331166 sequences. (Running on oeis4.)