|
| |
|
|
A067651
|
|
Numbers n such that sigma(n) = phi(prime(n)-1).
|
|
2
| |
|
|
1, 7, 19, 47, 115, 177, 280, 297, 340, 406, 470, 930, 1240, 1608, 1836, 2232, 2380, 2484, 4326, 8360, 33864, 166152, 216216, 220248, 299250, 394500
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,2
|
|
|
COMMENTS
| No further term below 4*10^6.
|
|
|
EXAMPLE
| sigma(19) = 20, prime(19) = 67, phi(66) = 20, hence 20 is a term.
|
|
|
PROG
| (PARI) m=400000; for(n=1, m, if(sigma(n)==eulerphi(prime(n)-1), print1(n, ", ")))
|
|
|
CROSSREFS
| Cf. A107815, A107816.
Sequence in context: A146403 A000491 A097039 * A090025 A003232 A018728
Adjacent sequences: A067648 A067649 A067650 * A067652 A067653 A067654
|
|
|
KEYWORD
| nonn,more
|
|
|
AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 23 2002
|
|
|
EXTENSIONS
| More terms from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Mar 02 2002, revised May 24 2005
|
| |
|
|
