A373453 Iterate the function x <- phi(sigma(x)). The sequence has the smallest member of cycles of length 3.

16, 1200, 15552, 67392, 272160, 69672960000

Offset: 1

Author

Jud McCranie, Jun 06 2024

Keywords

• nonn
• more

Comments

69672960000 is also a term in the sequence.

a(7) <= 2704853606400. The numbers 242595672883200000, 66217181184000000000 and 185577469193591193600 are also terms. - Giorgos Kalogeropoulos, Jun 18 2024

4672651788288000 is also a term. - Jud McCranie, Jun 18 2024

The sequence is complete through 10^13. - Jud McCranie, Sep 14 2024

Examples

			16 -> 30 -> 24 -> 16, so 16 (the smallest term) is in the sequence.
		

Links

• Richard R. Forberg, Additional terms, Nov 2024.

Crossrefs

Subsequence of A376256.

Cf. A001229, A095955, A095956, A373435, A373454.

Programs

PARI

isok(x) = my(y = eulerphi(sigma(x))); if (y > x, my(z = eulerphi(sigma(y))); if (z > x, x == eulerphi(sigma(z)))); \\ Michel Marcus, Jun 07 2024

Extensions

a(6) from Giorgos Kalogeropoulos, Jun 18 2024