A295502 a(n) = phi(5^n-1), where phi is Euler's totient function (A000010).

2, 8, 60, 192, 1400, 4320, 39060, 119808, 894240, 2912000, 24414060, 62208000, 610351560, 1959874560, 13154400000, 44043337728, 380537036928, 997843069440, 9485297382000, 25606963200000, 230106651919200, 748687423334400, 5959800062798400, 15138938880000000

Offset

1,1

Comments

Faye et al. prove that no term is of the form 5^k-1. - Michel Marcus, Jun 16 2024

Links

Max Alekseyev, Table of n, a(n) for n = 1..502

Bernadette Faye, Florian Luca, and Amadou Tall, On the equation phi(5^m-1)=5^n-1, Bull. Korean Math. Soc. 2015; 52(2): 513-524.

Eric Weisstein's World of Mathematics, Totient Function

Wikipedia, Euler's totient function

Formula

a(n) = n*A027741(n).

a(n) = A000010(A024049(n)). - Michel Marcus, Jun 16 2024

Mathematica

EulerPhi[5^Range[25] - 1] (* Paolo Xausa, Jun 18 2024 *)

Prog

(PARI) {a(n) = eulerphi(5^n-1)}

Crossrefs

Cf. A000010, A024049.

phi(k^n-1): A053287 (k=2), A295500 (k=3), A295501 (k=4), this sequence (k=5), A366623 (k=6), A366635 (k=7), A366654 (k=8), A366663 (k=9), A295503 (k=10), A366685 (k=11), A366711 (k=12).

Sequence in context: A203208 A181010 A197941 * A196076 A027278 A001415

Adjacent sequences: A295499 A295500 A295501 * A295503 A295504 A295505

Keyword

nonn

Author

Seiichi Manyama, Nov 22 2017

Status

approved