|
|
A210495
|
|
Numbers n such that d(n)*n + 1 is prime, d(n) = number of divisors of n.
|
|
1
|
|
|
1, 2, 3, 4, 5, 10, 11, 12, 15, 18, 22, 23, 24, 27, 29, 30, 32, 34, 39, 41, 42, 45, 52, 53, 54, 56, 57, 58, 63, 64, 68, 69, 76, 83, 84, 87, 89, 93, 96, 108, 110, 113, 115, 131, 142, 144, 147, 150, 152, 153, 156, 162, 165, 168, 170, 172, 173, 175, 177
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
This is the union of Sophie Germain primes and Sophie Germain nonprimes, so it might be called "Sophie Germain numbers".
|
|
LINKS
|
|
|
MAPLE
|
option remember;
local a;
if n = 1 then
1 ;
else
for a from procname(n-1)+1 do
if isprime(numtheory[tau](a)*a+1) then
return a;
end if;
end do:
end if;
|
|
MATHEMATICA
|
Select[Range[200], PrimeQ[# DivisorSigma[0, #]+1]&] (* Harvey P. Dale, Aug 26 2013 *)
|
|
PROG
|
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|