|
|
A066814
|
|
Smallest prime p such that (p-1) has n divisors, or 0 if no such prime exists.
|
|
3
|
|
|
2, 3, 5, 7, 17, 13, 0, 31, 37, 113, 0, 61, 0, 193, 401, 211, 65537, 181, 0, 241, 577, 13313, 0, 421, 1297, 12289, 4357, 2113, 0, 1009, 0, 1321, 25601, 2424833, 752734097, 1801, 0, 786433, 495617, 2161, 0, 4801, 0, 15361, 7057, 155189249, 0
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
The only primes p for which p-1 has a prime number of divisors are Fermat primes A019434.
|
|
LINKS
|
|
|
EXAMPLE
|
a(17)=65537 because DivisorSigma[0,65536]=17.
|
|
MATHEMATICA
|
it=Table[ p=Prime[ n ]; DivisorSigma[ 0, p-1 ], {n, 400000} ]; Flatten[ Position[ it, #, 1, 1 ]&/@Range[ 100 ]/.{}- > 0 ]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|