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A373454
Iterate the function x <- phi(sigma(x)). The sequence has the smallest member of cycles of length 4.
9
576, 41472, 2142720000, 3233260800
OFFSET
1,1
COMMENTS
130767436800000 is also a term. - Jud McCranie, Jun 18 2024
Terms are complete to 10^13. - Jud McCranie, Sep 14 2024
Terms also include 2590533833653034680320, 4911428805164059852800, 345401330417459527680000, 45369029282941832999731200, 1178793806496987670275686400000, 1241573383607207067648000000000, 3740981970485927435304960000000. - Richard R. Forberg, Oct 06 2024
EXAMPLE
576 -> 1512 -> 1280 -> 864 -> 576, so 576 (the smallest term) is in the sequence.
PROG
(PARI) isok(x) = my(y = eulerphi(sigma(x))); if (y > x, my(z = eulerphi(sigma(y))); if (z>x, x == eulerphi(sigma(eulerphi(sigma(z)))))); \\ Michel Marcus, Jun 07 2024
CROSSREFS
KEYWORD
nonn,more,changed
AUTHOR
Jud McCranie, Jun 06 2024
STATUS
approved