A049116 Repeatedly apply Euler phi to n; a(n) = highest power of 2 that is seen.

1, 2, 2, 4, 4, 2, 2, 8, 2, 4, 4, 4, 4, 2, 8, 16, 16, 2, 2, 8, 4, 4, 4, 8, 8, 4, 2, 4, 4, 8, 8, 32, 8, 16, 8, 4, 4, 2, 8, 16, 16, 4, 4, 8, 8, 4, 4, 16, 4, 8, 32, 8, 8, 2, 16, 8, 4, 4, 4, 16, 16, 8, 4, 64, 16, 8, 8, 32, 8, 8, 8, 8, 8, 4, 16, 4, 16, 8, 8, 32, 2, 16, 16, 8, 64, 4, 8, 16, 16, 8, 8, 8

Offset: 1

Author

Labos Elemer

Keywords

• nonn

Examples

			If n is a power of 2, then it is of largest exponent. If n=2400, then its phi-sequence is {2400,640,256,128,64,32,16,8,4,2,1}. The value of first power of 2 is 256. Thus a(2400)=256.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010.

Programs

Mathematica

Table[SelectFirst[NestWhileList[EulerPhi[#]&,n,#>1&],IntegerQ[Log[2,#]]&],{n,120}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 23 2019 *)