A071836 Numbers k such that the largest prime factor of k = prime(tau(k)).

3, 14, 21, 25, 35, 52, 114, 117, 152, 190, 266, 285, 325, 338, 343, 399, 418, 444, 464, 494, 507, 513, 627, 637, 646, 665, 666, 740, 741, 845, 969, 1036, 1045, 1183, 1184, 1235, 1272, 1463, 1573, 1590, 1615, 1628, 1665, 1729, 1850, 1859, 1924, 2116, 2120

Offset

1,1

Comments

Numbers k such that A006530(k) = A000040(A000005(k)).

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

666 = 2*3^2*37, tau(666) = 12, prime(12) = 37, hence 666 is a term.

Mathematica

Select[Range[2200], FactorInteger[#][[-1, 1]]==Prime[DivisorSigma[0, #]]&] (* Harvey P. Dale, Aug 13 2021 *)

Prog

(PARI) for(n=2, 3000, if(component(component(factor(n), 1), omega(n))==prime(numdiv(n)), print1(n, ", ")))
(PARI) is(k) = if(k > 1, my(f = factor(k)); f[#f~, 1] == prime(numdiv(f)), 0); \\ Amiram Eldar, Oct 27 2024

Crossrefs

Cf. A000005, A000040, A006530, A105555.

Sequence in context: A015639 A019000 A305090 * A361909 A300216 A258218

Adjacent sequences: A071833 A071834 A071835 * A071837 A071838 A071839

Keyword

easy,nonn

Author

Benoit Cloitre, Jun 08 2002

Status

approved