OFFSET
1,1
COMMENTS
Old name was "Solutions to {A094471[x]=prime} that is to {x; x*tau[x]-sigma[x]=prime}."
All terms after the first are even, because A094471(n) is even if n is odd. The first term == 2 (mod 4) is a(135) = 9653618. - Robert Israel, Nov 11 2015
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..100
EXAMPLE
n=8: 8*tau[8]-sigma[8]=8*4-15=32-15=17 is a prime, so 8 is here.
MAPLE
A094471:= n -> n*numtheory:-tau(n) - numtheory:-sigma(n):
select(t -> isprime(A094471(t)), 2*[3/2, $1..10^6]); # Robert Israel, Nov 11 2015
MATHEMATICA
Do[s=n*DivisorSigma[0, n]-DivisorSigma[1, n]; If[PrimeQ[s], Print[{n, s}]; ta[[u]]=n; tb[[u]]=s; u=u+1], {n, 1, 1000000}]; ta
Select[Range[215000], PrimeQ[# DivisorSigma[0, #]-DivisorSigma[1, #]]&] (* Harvey P. Dale, Dec 07 2021 *)
PROG
(PARI) isok(n) = isprime(n*numdiv(n)-sigma(n)); \\ Michel Marcus, Nov 12 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 15 2004
EXTENSIONS
Name modified by Tom Edgar, Nov 12 2015
STATUS
approved