A067893 Nonprimes k such that tau(k)*sigma(k) < prime(k) where tau(k) = A000005(k) and sigma(k) = A000203(k).

1, 25, 49, 77, 85, 91, 95, 115, 119, 121, 123, 125, 129, 133, 141, 143, 145, 155, 159, 161, 169, 177, 183, 185, 187, 194, 201, 202, 203, 205, 206, 209, 213, 214, 215, 217, 218, 219, 221, 226, 235, 237, 247, 249, 253, 254, 259, 262, 265, 267, 274, 278, 287

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Mathematica

Select[Range[300], !PrimeQ[#]&&DivisorSigma[0, #]DivisorSigma[1, #]<Prime[ #]&](* Harvey P. Dale, Nov 09 2017 *)

Prog

(PARI) isok(k) = !isprime(k) && (numdiv(k)*sigma(k) < prime(k)); \\ Michel Marcus, Jul 18 2019

Crossrefs

Cf. A000005, A000040, A000203.

Sequence in context: A103214 A067778 A350061 * A067794 A377884 A068874

Adjacent sequences: A067890 A067891 A067892 * A067894 A067895 A067896

Keyword

easy,nonn

Author

Benoit Cloitre, Mar 02 2002

Extensions

Typo in definition corrected by Jonathan Sondow, Nov 20 2012

Status

approved