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
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
KEYWORD
nonn,more
AUTHOR
Michel Marcus, Aug 22 2018
STATUS
approved