A366821 -id:A366821 - cp's OEIS frontend

A377678 a(n) = phi(n^n - n) where phi is the Euler totient function.

1, 8, 72, 768, 12400, 217728, 7112448, 94371840, 2594586816, 69139840000, 2584376931840, 58779453358080, 4367959006806720, 100089965305451520, 3251736576000000000, 200445251536048619520, 12343971160877345120064, 422076038504126628593664

Offset: 2

Sean A. Irvine, Nov 03 2024

nonn

Amiram Eldar, Table of n, a(n) for n = 2..115

Cf. A000010, A061190, A366821, A372229, A372599, A377674, A377675, A377676, A377677.

a[n_] := EulerPhi[n^n - n]; Array[a, 20, 2] (* Amiram Eldar, Nov 04 2024 *)

PARI
```
a(n) = eulerphi(n^n-n);
```

a(n) = A000010(A061190(n)).

A366822 a(n) is phi(n^n + 1) where phi is the Euler totient function.

Original entry on oeis.org

1, 1, 4, 12, 256, 1040, 41472, 407680, 16515072, 152845056, 9897840000, 89493288192, 8732596764672, 129785922489600, 10576701872701440, 210729768933600000, 18446676793287966720, 275746753962112254720, 28084363369373740400640, 791359800910482004224000

Offset: 0

Sean A. Irvine, Oct 24 2023

nonn

Robert G. Wilson v, Table of n, a(n) for n = 0..72
Eric Weisstein's World of Mathematics, Sierpinski Number of the First Kind

Cf. A000010, A014566, A064447, A366821.

{1}~Join~Array[EulerPhi[#^# + 1] &, 19] (* Michael De Vlieger, Oct 24 2023 *)

PARI
```
a(n) = eulerphi(n^n+1);
```

a(n) = A000010(A014566(n)).

cp's OEIS Frontend

A377678 a(n) = phi(n^n - n) where phi is the Euler totient function.

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