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A295502
a(n) = phi(5^n-1), where phi is Euler's totient function (A000010).
14
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
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
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
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
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 22 2017
STATUS
approved