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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. 6
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 (list; graph; refs; listen; history; text; internal format)
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-Fran├žois Alcover, Nov 01 2020 *)

CROSSREFS

Cf. A000010, A008344.

Sequence in context: A328598 A284010 A278082 * A068773 A234312 A244136

Adjacent sequences:  A327439 A327440 A327441 * A327443 A327444 A327445

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Sep 12 2019

STATUS

approved

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Last modified January 27 01:03 EST 2021. Contains 340443 sequences. (Running on oeis4.)