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

Author

Michel Marcus, Aug 22 2018

Keywords

• nonn
• more

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

• 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).