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

1,1

Links

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

Example

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

Mathematica

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

Prog

(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

Crossrefs

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

Sequence in context: A006618 A184551 A190039 * A106563 A106574 A171125

Adjacent sequences: A066071 A066072 A066073 * A066075 A066076 A066077

Keyword

nonn

Author

Labos Elemer, Dec 03 2001

Status

approved