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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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified August 6 00:03 EDT 2024. Contains 374957 sequences. (Running on oeis4.)