A074693 a(1) = 1, a(n) = a(n-1) + phi(a(n-1)).

1, 2, 3, 5, 9, 15, 23, 45, 69, 113, 225, 345, 521, 1041, 1733, 3465, 4905, 7497, 11529, 18009, 29097, 47817, 71577, 114777, 184761, 307881, 482841, 804573, 1212813, 1854333, 2993517, 4953069, 7752429, 12826269, 21376953, 34207353, 55027593, 91712493, 152705493

Offset: 1

Author

Benoit Cloitre, Sep 03 2002

Keywords

• easy
• nonn

Comments

Partial sums of A165931. - Jaroslav Krizek, Sep 30 2009

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..500 (first 300 terms from T. D. Noe)

Crossrefs

Cf. A000010, A165931.

Programs

Maple

a:= proc(n) option remember; `if`(n=1, 1,
      numtheory[phi](a(n-1))+a(n-1))
    end:
seq(a(n), n=1..50);  # Alois P. Heinz, Oct 02 2020

Mathematica

NestList[# + EulerPhi@ # &, 1, 36] (* Robert G. Wilson v, Mar 02 2011 *)

Formula

1 < a(n+1)/a(n) <= 2 . Does limit a(n+1)/a(n) exist ?