A053038 The first (largest) power of 2 arising in the iteration-sequence when A051953 (the cototient function) is repeatedly applied starting with n!.

1, 2, 4, 16, 32, 128, 512, 4096, 16384, 2048, 8192, 65536, 16384, 65536, 8388608, 134217728, 8388608, 8388608, 16777216, 2097152, 8388608, 268435456, 4398046511104, 70368744177664, 67108864, 67108864, 67108864, 68719476736

Offset: 1

Author

Labos Elemer, Feb 24 2000

Keywords

• nonn

Examples

			For n = 10, initial value = 10! = 3628800; after the following initial terms {3628800, 2799360, 2052864, 1430784, 974592, 656640, 490752, 329472,  237312, 158976, 108288, 72960, 54528, 36608, 21248, 10752, 7680, 5632, 3072, ...}, the first power of 2 is 2048 = cototient(3072). Therefore a(10) = 2048.
		

Crossrefs

Cf. A051953, A053475, A053039.

Programs

Mathematica

Table[NestWhile[# - EulerPhi@ # &, n!, ! IntegerQ@ Log2@ # &], {n, 28}] (* Michael De Vlieger, Aug 15 2017 *)