A132857 a(0)=1. a(n) = phi(n+a(n-1)), for n>=1, where phi(m) is the number of positive integers which are <= m and are coprime to m.

1, 1, 2, 4, 4, 6, 4, 10, 6, 8, 6, 16, 12, 20, 16, 30, 22, 24, 12, 30, 20, 40, 30, 52, 36, 60, 42, 44, 24, 52, 40, 70, 32, 48, 40, 40, 36, 72, 40, 78, 58, 60, 32, 40, 24, 44, 24, 70, 58, 106, 48, 60, 48, 100, 60, 88, 48, 48, 52, 72, 40, 100, 54, 72, 64, 84, 40, 106, 56, 100

Offset

0,3

Links

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Example

a(8) + 9 = 6 + 9 = 15. There are 8 positive integers that are <= 15 and are relatively prime to 15. So a(9) = 8.

Mathematica

a = {1}; For[n = 1, n < 90, n++, AppendTo[a, EulerPhi[n + a[[ -1]]]]]; a (* Stefan Steinerberger, Nov 24 2007 *)
nxt[{n_, a_}]:={n+1, EulerPhi[n+1+a]}; NestList[nxt, {0, 1}, 70][[All, 2]] (* Harvey P. Dale, Apr 23 2022 *)

Crossrefs

Sequence in context: A062011 A375373 A225520 * A365264 A152782 A307119

Adjacent sequences: A132854 A132855 A132856 * A132858 A132859 A132860

Keyword

nonn

Author

Leroy Quet, Nov 21 2007

Extensions

More terms from Stefan Steinerberger, Nov 24 2007

Status

approved