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A165931 a(1) = 1, for n > 1: a(n) = phi(sum of the previous terms) where phi(k) is Euler's totient function 1
1, 1, 1, 2, 4, 6, 8, 22, 24, 44, 112, 120, 176, 520, 692, 1732, 1440, 2592, 4032, 6480, 11088, 18720, 23760, 43200, 69984, 123120, 174960, 321732, 408240, 641520 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(1) = 1, for n > 1: a(n) = phi(sum_(i = 1 ... n - 1) a(i)) = A000010(sum_(i = 1 ... n - 1) a(i)). a(n) = inverse of partial sums of A074693(n), i.e. a(1) = A074693(1), for n > 1: a(n) = A074693(n) - A074693(n - 1), i.e. first differences of A074693.

LINKS

Table of n, a(n) for n=1..30.

EXAMPLE

For n = 4 the a(4) = phi(a(1) + a(2) + a(3)) = phi(1 + 1 + 1) = phi(3) = 2.

MATHEMATICA

a[1] := 1; a[n_] := a[n] = EulerPhi[Plus @@ Table[a[m], {m, n - 1}]]; Table[a[n], {n, 30}]

CROSSREFS

Sequence in context: A230105 A045926 A045927 * A321600 A081939 A082615

Adjacent sequences:  A165928 A165929 A165930 * A165932 A165933 A165934

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Sep 30 2009

EXTENSIONS

Terms double-checked by Alonso del Arte, Oct 12 2009

STATUS

approved

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Last modified August 20 22:45 EDT 2019. Contains 326155 sequences. (Running on oeis4.)