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

0,4

Links

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

Maple

a:= proc(n) option remember; `if`(n<1, 0, ((s, t)-> s+
     `if`(s<t, t, -t))(a(n-1), numtheory[phi](n)))
    end:
seq(a(n), n=0..80);  # Alois 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 *)

Crossrefs

Cf. A000010, A008344.

Sequence in context: A328598 A284010 A278082 * A068773 A340692 A234312

Adjacent sequences: A327439 A327440 A327441 * A327443 A327444 A327445

Keyword

nonn

Author

N. J. A. Sloane, Sep 12 2019

Status

approved