A373454 Iterate the function x <- phi(sigma(x)). The sequence has the smallest member of cycles of length 4.

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

Links

Table of n, a(n) for n=1..4.

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

Cf. A001229, A095955. A095956, A373435, A373453.

Sequence in context: A223301 A168660 A268903 * A249688 A079396 A299414

Adjacent sequences: A373451 A373452 A373453 * A373455 A373456 A373457

Keyword

nonn,more

Author

Jud McCranie, Jun 06 2024

Status

approved