A327442 a(0) = 0; thereafter a(n) = a(n-1) + phi(n) if phi(n) > a(n-1), otherwise a(n) = a(n-1) - phi(n), where phi is the Euler phi-function A000010.

0, 1, 0, 2, 0, 4, 2, 8, 4, 10, 6, 16, 12, 0, 6, 14, 6, 22, 16, 34, 26, 14, 4, 26, 18, 38, 26, 8, 20, 48, 40, 10, 26, 6, 22, 46, 34, 70, 52, 28, 12, 52, 40, 82, 62, 38, 16, 62, 46, 4, 24, 56, 32, 84, 66, 26, 2, 38, 10, 68, 52, 112, 82, 46, 14, 62, 42, 108, 76, 32, 8, 78, 54, 126, 90

Offset: 0

Author

N. J. A. Sloane, Sep 12 2019

Keywords

• nonn

Links

• N. J. A. Sloane, Table of n, a(n) for n = 0..9999

Crossrefs

Cf. A000010, A008344.

Programs

Maple

a:= proc(n) option remember; `if`(n<1, 0, ((s, t)-> s+
     `if`(sAlois P. Heinz, Jan 11 2020

Mathematica

a[0] = 0; a[n_] := a[n] = With[{phi = EulerPhi[n], a1 = a[n-1]}, If[phi>a1, a1+phi, a1-phi]];
a /@ Range[0, 80] (* Jean-François Alcover, Nov 01 2020 *)
nxt[{n_,a_}]:=Module[{ph=EulerPhi[n+1]},{n+1,If[ph>a,a+ph,a-ph]}]; NestList[nxt,{0,0},80][[;;,2]] (* Harvey P. Dale, Jun 14 2023 *)