A326824 a(1) = 1; a(n) = Sum_{d|n, d < n} phi(n/d) * d * a(d).

1, 1, 2, 4, 4, 12, 6, 24, 18, 32, 10, 124, 12, 60, 72, 240, 16, 336, 18, 440, 132, 140, 22, 2088, 100, 192, 378, 1044, 28, 2096, 30, 4320, 300, 320, 312, 9636, 36, 396, 408, 10384, 40, 5040, 42, 3500, 3000, 572, 46, 61584, 294, 3920, 672, 5544, 52, 23148, 680

Offset: 1

Author

Ilya Gutkovskiy, Feb 23 2020

Keywords

• nonn

Crossrefs

Cf. A000010, A001710, A006579, A006874, A018804, A165552.

Programs

Mathematica

a[1] = 1; a[n_] := Sum[If[d < n, EulerPhi[n/d] d a[d], 0], {d, Divisors[n]}]; Table[a[n], {n, 1, 55}]
a[1] = 1; a[n_] := Sum[GCD[n, k] a[GCD[n, k]], {k, 1, n - 1}]; Table[a[n], {n, 1, 55}]

Formula

a(1) = 1; a(n) = Sum_{k=1..n-1} gcd(n, k) * a(gcd(n, k)).