A377677
a(n) is the sum of the divisors of n^n - n.
Original entry on oeis.org
3, 60, 728, 10416, 116064, 2837120, 36990720, 1452853584, 27615698352, 965243666880, 23861701899840, 1355882884941312, 20758574413420992, 1604569397488307712, 93340493714183159808, 3135286584767445151680, 90560273718863022770592, 8284620870197084160000000
Offset: 2
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a[n_] := DivisorSigma[1, n^n - n]; Array[a, 20, 2] (* Amiram Eldar, Nov 04 2024 *)
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a(n) = sigma(n^n-n);
A366821
a(n) is phi(n^n-1) where phi is the Euler totient function.
Original entry on oeis.org
2, 12, 128, 1400, 30240, 264992, 6635520, 141087744, 5890320000, 114117380608, 4662793175040, 99053063903040, 5470524984113280, 167080949856000000, 9208981628670443520, 413582117375670921216, 29531731481729468006400, 659473218553437863041320
Offset: 2
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a:= n-> numtheory[phi](n^n-1):
seq(a(n), n=2..20); # Alois P. Heinz, Oct 26 2023
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Array[EulerPhi[#^# - 1] &, 18, 2] (* Michael De Vlieger, Oct 24 2023 *)
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a(n) = eulerphi(n^n-1);
A366820
a(n) is the sum of the divisors of n^n + 1.
Original entry on oeis.org
3, 3, 6, 56, 258, 6264, 52136, 1559520, 17041416, 706911048, 10102223208, 706019328000, 9101898907920, 519285252355776, 11672709747324912, 880565163670372352, 18446811354131136516, 1792353900753729655758, 54357680125881245248800, 4154723599066412190910560
Offset: 0
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