A341710 a(n) = A120963(n)/2.

1, 3, 5, 12, 19, 39, 59, 112, 165, 292, 419, 710, 1001, 1629, 2257, 3567, 4877, 7505, 10133, 15266, 20399, 30140, 39881, 57983, 76085, 108981, 141877, 200625, 259373, 362433, 465493, 643653, 821813, 1125269, 1428725, 1939149, 2449573, 3297411, 4145249, 5538254

Offset: 1

Author

N. J. A. Sloane, Feb 19 2021

Keywords

• nonn

Crossrefs

Cf. A120963, A341711, A341712.

Programs

Maple

with(numtheory):
b:= proc(n) option remember; nops(invphi(n)) end:
a:= proc(n) option remember; `if`(n=0, 1/2, add(
      a(n-j)*add(d*b(d), d=divisors(j)), j=1..n)/n)
    end:
seq(a(n), n=1..40);  # Alois P. Heinz, Feb 19 2021

Mathematica

terms = 40;
S[m_] := S[m] = CoefficientList[Product[1/(1 - x^EulerPhi[k]),
     {k, 1, m*terms}] + O[x]^(terms+1), x]/2 // Rest;
S[m = 1];
S[m++];
While[S[m] != S[m-1], m++];
S[m] (* Jean-François Alcover, May 12 2022 *)