A332791 - OEIS

A332791

a(1) = 1; a(n+1) = Sum_{d|n} phi(d) * a(d).

1, 1, 2, 5, 12, 49, 104, 625, 2512, 15077, 60358, 603581, 2414438, 28973257, 173840168, 1390721397, 11125773688, 178012379009, 1068074289230, 19225337206141, 153802697709496, 1845632372514581, 18456323725749392, 406039121966486625, 3248312975734309938

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OFFSET

1,3

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 1..495

FORMULA

a(1) = 1; a(n+1) = Sum_{k=1..n} a(n/gcd(n, k)).

a(n) = Sum_{k=1..n} a(gcd(n,k))*phi(gcd(n,k))/phi(n/gcd(n,k)). - Richard L. Ollerton, May 07 2021

MATHEMATICA

a[1] = 1; a[n_] := Sum[EulerPhi[d] a[d], {d, Divisors[n - 1]}]; Table[a[n], {n, 1, 25}]

a[1] = 1; a[n_] := a[n] = Sum[a[(n - 1)/GCD[n - 1, k]], {k, 1, n - 1}]; Table[a[n], {n, 1, 25}]

CROSSREFS