A066074 Primes arising in A066073.

11, 17, 23, 23, 41, 31, 59, 41, 71, 47, 53, 47, 59, 89, 83, 71, 71, 97, 71, 79, 89, 167, 103, 83, 113, 139, 167, 223, 107, 131, 179, 233, 167, 127, 251, 191, 151, 239, 181, 179, 359, 167, 223, 311, 251, 239, 269, 191, 167, 179, 227, 233, 191, 239, 191, 293

Offset: 1

Author

Labos Elemer, Dec 03 2001

Keywords

• nonn

Examples

			p=71 appears in the sequence at 9th, 16th, 17th and 19th positions as -1+sigma(x) for x=30, 46, 51, 55.
		

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000203, A058340, A066071, A066072, A066073, A066074, A066075, A066076, A066077, A066080.

Programs

Mathematica

Do[s=-1+DivisorSigma[1, n]; If[PrimeQ[s]&&!PrimeQ[n], Print[s]], {n, 1, 256}]

PARI

{ n=0; for (m=1, 10^9, if (!isprime(m) && isprime(p=sigma(m) - 1), write("b066074.txt", n++, " ",p); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 10 2009

PARI

lista(nn) = forcomposite(n=1, nn, if (isprime(p=(sigma(n)-1)), print1(p, ", "))); \\ Michel Marcus, Jan 05 2018