|
|
A252021
|
|
Primes p such that (p - 1)/tau(p - 1) is also prime.
|
|
2
|
|
|
13, 19, 41, 61, 89, 137, 157, 229, 233, 277, 349, 373, 569, 709, 733, 809, 853, 857, 877, 997, 1049, 1069, 1097, 1193, 1213, 1237, 1433, 1669, 1789, 1913, 2153, 2293, 2389, 2677, 2749, 2777, 2797, 3209, 3229, 3253, 3373, 3449, 3517, 3593, 3733, 3833, 3929, 4073, 4457, 4549, 4597, 4793, 4813, 4909, 4937, 5197, 5273
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
a(1) = 13, since 12/tau(12) = 2.
a(2) = 19, since 18/tau(18) = 3.
a(4) = 61, since 60/tau(60) = 5.
|
|
MATHEMATICA
|
Select[Prime[Range[1000]], PrimeQ[(# - 1)/DivisorSigma[0, # - 1]] &]
|
|
PROG
|
(Magma) [p:p in PrimesUpTo(5300)| ((p-1) mod NumberOfDivisors(p-1) eq 0) and IsPrime((p-1) div NumberOfDivisors(p-1)) ]; // Marius A. Burtea, Dec 30 2019
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|