|
| |
|
|
A066075
|
|
Number of solutions x to prime(n) = sigma(x) - 1, where prime(n) is the n-th prime.
|
|
11
|
|
|
|
1, 1, 1, 1, 2, 1, 2, 1, 3, 1, 2, 1, 3, 1, 3, 2, 3, 1, 1, 5, 1, 2, 3, 3, 2, 1, 2, 2, 1, 2, 2, 2, 1, 2, 1, 2, 1, 1, 6, 1, 4, 2, 5, 1, 1, 1, 1, 3, 3, 1, 3, 7, 1, 6, 1, 2, 3, 2, 1, 1, 1, 3, 2, 4, 1, 1, 1, 1, 1, 1, 1, 9, 1, 1, 1, 6, 2, 1, 1, 1, 4, 1, 8, 4, 2, 2, 3, 1, 1, 1, 3, 9, 1, 2, 1, 10, 1, 2, 1, 1
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,5
|
|
|
COMMENTS
|
prime(n) itself is always the largest solution, but often composite solutions also occur.
If a(n)=1, then the single solution is prime(n).
|
|
|
LINKS
|
Harry J. Smith, Table of n, a(n) for n = 1..1000
|
|
|
EXAMPLE
|
n=96, p(96)=503, 503=sigma(x)-1 has 10 solutions together with 503: {204, 220, 224, 246, 284, 286, 334, 415, 451, 503} so a(96)=10.
|
|
|
PROG
|
(PARI) { for (n=1, 1000, a=1; for (x=1, prime(n) - 1, if (prime(n) == (sigma(x) - 1), a++)); write("b066075.txt", n, " ", a) ) } \\ Harry J. Smith, Nov 10 2009
|
|
|
CROSSREFS
|
Number of solutions to A000040(n) = A000203(x) - 1.
Cf. A000040, A000203, A058340, A066071, A066072, A066073, A066074, A066075, A066076, A066077, A066080.
Sequence in context: A319841 A336099 A290090 * A359211 A072347 A351034
Adjacent sequences: A066072 A066073 A066074 * A066076 A066077 A066078
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Labos Elemer, Dec 03 2001
|
|
|
STATUS
|
approved
|
| |
|
|
