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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
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
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. A272930 (analog for sigma), A318272 (analog for infinitary sigma).
Sequence in context: A246304 A063286 A133230 * A318272 A244476 A292202
KEYWORD
nonn,more
AUTHOR
Michel Marcus, Aug 22 2018
STATUS
approved