A200811 Iterate k -> d(k) until an odd prime is reached, starting from the n-th composite.

3, 3, 3, 3, 3, 3, 3, 3, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 7, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3

Offset

1,1

Comments

a(n) is not 3 for n in {9, 45, 58, 89, 128, 163, 168, ...} = A396521.

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Tímea Csajbók and János Kasza, Iterating the tau-function, Annales Univ. Sci. Budapest., Sec. Math. 35 (2011), pp. 83-93.

Mathematica

Map[NestWhile[DivisorSigma[0, #] &, #, CompositeQ] &, Select[Range[150], CompositeQ]] (* Paolo Xausa, Jun 02 2026 *)

Crossrefs

Cf. A000005, A200810, A200815, A396521.

Sequence in context: A053388 A372511 A091786 * A339055 A331134 A303168

Adjacent sequences: A200808 A200809 A200810 * A200812 A200813 A200814

Keyword

nonn,changed

Author

Charles R Greathouse IV, Nov 23 2011

Status

approved