A055813 Primes arising in A064205.

2, 5, 19, 263, 373, 1033, 65551, 123833, 283553, 292993, 2197633, 5778673, 12795193, 10500613, 19980283, 32213033, 36978853, 72494813, 140724953, 164119063, 183105509, 193710277, 320210941, 450065801, 268354393, 496922891, 506906473, 1333406021

Offset: 1

Author

Labos Elemer, Nov 22 2001

Keywords

• nonn

Examples

			a(3) = 19 since, for A064205(3) = 8, sigma(8)+tau(8) = 15+4 = 19, a prime number. - _Michael De Vlieger_, Dec 17 2016
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..5000 (terms 1..276 from Michel Marcus)

Crossrefs

Cf. A007503, A064205.

Programs

Mathematica

Select[Table[Total@ Map[DivisorSigma[#, n] &, {0, 1}], {n, 10^7}], PrimeQ] (* Michael De Vlieger, Dec 17 2016 *)

PARI

lista(nn) = for (n=1, nn, if (isprime(p=sigma(n) + numdiv(n)), print1(p, ", "))); \\ Michel Marcus, Dec 18 2016

Formula

a(n) = A007503(A064205(n)). - Amiram Eldar, Dec 06 2022