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A126974 a(1)=0. a(2)=1. a(n) = a(d(n)) + a(phi(n)), where d(n) = A000005(n), phi(n) = A000010(n). 1
0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 7, 8, 7, 9, 10, 11, 8, 9, 10, 10, 9, 10, 12, 12, 10, 11, 11, 12, 12, 13, 14, 13, 13, 15, 13, 14, 11, 15, 16, 17, 13, 14, 14, 16, 12, 13, 16, 15, 14, 17, 16, 17, 14, 19, 18, 16, 14, 15, 17, 18, 15, 17, 19, 19, 16, 17, 18, 17, 18, 19, 19, 20, 16, 20 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Question: With what numbers the gaps (horizontal stripes) in the scatter plot are associated? - Antti Karttunen, Jul 12 2017

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

MAPLE

with(numtheory): a[1]:=0: a[2]:=1: for n from 3 to 90 do a[n]:=a[tau(n)]+a[phi(n)] od: seq(a[n], n=1..90); # Emeric Deutsch, Mar 24 2007

MATHEMATICA

f[l_List] := Block[{n = Length[l] + 1}, Append[l, l[[DivisorSigma[0, n]]] + l[[EulerPhi[n]]]]]; Nest[f, {0, 1}, 75] (* Ray Chandler, Mar 24 2007 *)

a[n_] := a[n] = If[n <= 2, n - 1, a[DivisorSigma[0, n]] + a[EulerPhi@ n]]; Array[a, 75] (* Michael De Vlieger, Jul 12 2017 *)

PROG

(PARI) A126974(n) = if(n<3, n-1, A126974(numdiv(n))+ A126974(eulerphi(n))); \\ Antti Karttunen, Jul 12 2017

CROSSREFS

Cf. A000005, A000010.

Sequence in context: A108872 A147847 A268680 * A089058 A282717 A303735

Adjacent sequences:  A126971 A126972 A126973 * A126975 A126976 A126977

KEYWORD

nonn,look

AUTHOR

Leroy Quet, Mar 20 2007

EXTENSIONS

More terms from Emeric Deutsch and Ray Chandler, Mar 24 2007

STATUS

approved

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Last modified August 11 08:05 EDT 2020. Contains 336422 sequences. (Running on oeis4.)