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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
OFFSET
0,4
LINKS
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
Sequence in context: A328598 A284010 A278082 * A068773 A340692 A234312
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Sep 12 2019
STATUS
approved