

A189394


Highly composite numbers whose number of divisors is also a highly composite number.


1



1, 2, 6, 12, 60, 360, 1260, 2520, 5040, 55440, 277200, 720720, 3603600, 61261200, 2205403200, 293318625600, 6746328388800, 195643523275200
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

Both n and d(n) are highly composite numbers.
It is extremely likely that this sequence is complete. The highly composite numbers have a very special form. The number of divisors of a large HCN has a high power of 2 in its factorization  which is not the form of an HCN.  T. D. Noe, Apr 21 2011


LINKS

Table of n, a(n) for n=1..18.
A. Flammenkamp, Highly composite numbers


EXAMPLE

d(60) = 12; both 60 and 12 are highly composite numbers


MATHEMATICA

(* First run program at A002182 *) Select[A002182, MemberQ[A002182, DivisorSigma[0, #]] &] (* Alonso del Arte, Apr 21 2011 *)


CROSSREFS

Cf. A002182, A002183, A141320.
Sequence in context: A072489 A072487 A254232 * A182862 A072938 A160274
Adjacent sequences: A189391 A189392 A189393 * A189395 A189396 A189397


KEYWORD

nonn,more


AUTHOR

Krzysztof Ostrowski, Apr 21 2011


EXTENSIONS

Typo in a(15) corrected by Ben Beer, Jul 20 2016


STATUS

approved



