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

Author

Leroy Quet, Nov 21 2007

Keywords

• nonn

Examples

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

Links

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

Programs

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 *)

Extensions

More terms from Stefan Steinerberger, Nov 24 2007