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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A107816 a(n) = sigma(A067651(n)). 2
1, 8, 20, 48, 144, 240, 720, 480, 756, 720, 864, 2304, 2880, 4080, 5040, 6240, 6048, 6720, 9984, 21600, 90720, 506880, 806400, 748800, 973440, 1153152 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that n = sigma(k) = phi(prime(k)-1) for some k.

Values of k are in A067651, values of prime(k) are in A107815.

LINKS

Table of n, a(n) for n=1..26.

EXAMPLE

a(3) = sigma(A067651(3)) = sigma(19) = 20.

PROG

(PARI) m=400000; for(n=1, m, s=sigma(n); if(s==eulerphi(prime(n)-1), print1(s, ", ")))

CROSSREFS

Cf. A067651, A107815.

Sequence in context: A273266 A273304 A169878 * A205219 A232401 A036835

Adjacent sequences:  A107813 A107814 A107815 * A107817 A107818 A107819

KEYWORD

nonn,more

AUTHOR

Klaus Brockhaus, May 24 2005

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 September 25 03:11 EDT 2021. Contains 347651 sequences. (Running on oeis4.)