A318242 a(n) is the least k such that A188999(A188999(k)) = n*k, where A188999 is the bi-unitary sigma function, or 0 if no such k exists.

1, 2, 8, 15, 24, 42, 240, 648, 168, 480, 321408, 4320, 57120, 103680, 1827840, 23591520, 898128000, 374250240

Offset

1,2

Comments

It is also known that a(20) = 11975040.

Then for higher indices n, we have:

a(19) <= 5235707393280;

a(21) <= 49110437376000;

a(22) <= 106780561395056640;

a(24) <= 1099525819392000;

a(25) <= 41252767395840;

a(26) <= 202768780032000.

Links

Table of n, a(n) for n=1..18.

Tomohiro Yamada, 2 and 9 are the only biunitary superperfect numbers, arXiv:1705.00189 [math.NT], 2017. See Table 1.

Tomohiro Yamada, 2 and 9 are the only biunitary superperfect numbers, Annales Univ. Sci. Budapest., Sec. Comp., Volume 48 (2018). See Table 1.

Crossrefs

Cf. A188999, A318175.

Cf. A272930 (analog for sigma), A318272 (analog for infinitary sigma).

Sequence in context: A246304 A063286 A133230 * A318272 A244476 A292202

Adjacent sequences: A318239 A318240 A318241 * A318243 A318244 A318245

Keyword

nonn,more

Author

Michel Marcus, Aug 22 2018

Status

approved