OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..5000 (terms 1..276 from Michel Marcus)
FORMULA
EXAMPLE
a(3) = 19 since, for A064205(3) = 8, sigma(8)+tau(8) = 15+4 = 19, a prime number. - Michael De Vlieger, Dec 17 2016
MATHEMATICA
Select[Table[Total@ Map[DivisorSigma[#, n] &, {0, 1}], {n, 10^7}], PrimeQ] (* Michael De Vlieger, Dec 17 2016 *)
PROG
(PARI) lista(nn) = for (n=1, nn, if (isprime(p=sigma(n) + numdiv(n)), print1(p, ", "))); \\ Michel Marcus, Dec 18 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Nov 22 2001
STATUS
approved