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A342607 a(n) = Sum_{d|n} phi(d)^(n-d). 3
1, 2, 2, 3, 2, 11, 2, 19, 66, 1027, 2, 835, 2, 279939, 1052674, 69635, 2, 10114563, 2, 1074855939, 78364426242, 100000000003, 2, 4315152387, 1099511627778, 106993205379075, 101559973445634, 21937029021319171, 2, 1162183941554179, 2, 562950221856771, 10000000000001073741826 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(n) = Sum_{k=1..n} phi(n/gcd(k,n))^(n - n/gcd(k,n) - 1).
G.f.: Sum_{k>=1} x^k/(1 - (phi(k) * x)^k).
If p is prime, a(p) = 2.
MATHEMATICA
a[n_] := DivisorSum[n, EulerPhi[#]^(n - #) &]; Array[a, 30] (* Amiram Eldar, Mar 17 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, eulerphi(d)^(n-d));
(PARI) a(n) = sum(k=1, n, eulerphi(n/gcd(k, n))^(n-n/gcd(k, n)-1));
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-(eulerphi(k)*x)^k)))
CROSSREFS
Sequence in context: A162733 A016003 A087139 * A226422 A016005 A016006
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 16 2021
STATUS
approved

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Last modified July 19 19:50 EDT 2024. Contains 374436 sequences. (Running on oeis4.)