A373739 a(n) is the smallest number that is in a cycle of length n when iterating x <- phi(sigma(x)).

1, 4, 16, 576

Offset: 1

Author

Jud McCranie, Jun 15 2024

Keywords

• nonn
• more
• hard

Comments

Terms in a cycle are distinct, i.e., going twice around a cycle of length 3 is not considered a cycle of length 6.

Other terms: a(5) <= 339026688000000, a(6) = 1800, a(8) <= 12959170560000, a(9) = 113218560, a(11) = 326592, a(12) = 5033164800, a(15) = 40255488, a(18) <= 150493593600, a(21) = 12227604480, a(22) <= 1316603904000.

Examples

			16 -> 24 -> 30 -> 16, 16 is the smallest member of any cycle of length 3, so a(3)=16.
		

Crossrefs

Cf. A062401, A095955, A095956, A373435, A373453, A373454.