|
| |
|
|
A066881
|
|
Numbers n such that sigma(phi(n))/sigma(n) is an integer >= 4.
|
|
2
|
|
|
|
121679, 1043909, 2350171, 2918263, 3396103, 3566807, 3688067, 4019467, 4562827, 5963407, 7300697, 7485979, 7853933, 8103301, 8364151, 9237779, 9514213, 9638527, 10531123, 11094619, 11384447, 12721937, 13576267, 15331313
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
COMMENTS
|
Conjecture: all natural numbers 1,2,3,..n will eventually occur among the integer values of sigma(phi(n))/sigma(n).
|
|
|
LINKS
|
Harry J. Smith, Table of n, a(n) for n=1,...,370
|
|
|
EXAMPLE
|
a(1)=121679 because sigma(phi(121679))/sigma(121679) = 4.
|
|
|
MAPLE
|
for n from 1 do spn := numtheory[sigma](numtheory[phi](n)) ; sn := numtheory[sigma](n) ; if spn mod sn = 0 then if spn/sn >= 4 then print(n, spn/sn) fi; fi; od: [From R. J. Mathar, Oct 01 2008]
|
|
|
PROG
|
(PARI) { n=0; for (m=1, 10^10, if((e=sigma(eulerphi(m))) % (s=sigma(m)) == 0 && e/s >= 4, write("b066881.txt", n++, " ", m); if (n==1000, return)) ) } [From Harry J. Smith, Apr 03 2010]
|
|
|
CROSSREFS
|
Cf. A066817.
Cf. A067383, A067382. [From R. J. Mathar, Oct 01 2008]
Sequence in context: A068136 A135495 A067384 * A048903 A185864 A115545
Adjacent sequences: A066878 A066879 A066880 * A066882 A066883 A066884
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Jason Earls (zevi_35711(AT)yahoo.com), Jan 22 2002
|
|
|
EXTENSIONS
|
Terms a(16) etc. from R. J. Mathar, Oct 01 2008
|
|
|
STATUS
|
approved
|
| |
|
|
