A266276 a(n) is the smallest number k such that phi(k) = n*phi(k-1).

2, 3, 7, 1261, 11242771

Offset: 1

Author

Jaroslav Krizek, Jan 26 2016

Keywords

• nonn
• hard
• more

Comments

a(n) >= A266269(n). - Max Alekseyev, Jan 26 2025

Examples

			a(3) = 7 because 7 is the smallest number k such that phi(k) = n*phi(k-1); phi(7) = 6 =3*phi(6) = 3*2.
		

Crossrefs

Sequences of numbers n such that phi(n) = k*phi(n-1): {A001274 + 1} for k=1; A171271 = {A050472 + 1} for k=2; A266268 = {A067143 + 1} for k=3; A268126 = {A172314 + 1} for k=4; {A201253 + 1} for k=5.

Cf. A000010, A091439, A091456, A266269.

Programs

Magma

a:=func; [a(n):n in[1..5]];

PARI

a(n) = my(k=2, epk=1, enk); while ((enk=eulerphi(k)) != n*epk, epk = enk; k++); k; \\ Michel Marcus, Feb 20 2020