A117820 Numbers such that UnitaryPhi(2*UnitaryPhi(n)) = n.

1, 3, 15, 216, 255, 1080, 1728, 8640, 18360, 19344, 65535, 146880, 182880, 309504, 1226400, 2967888, 3456000, 4718520, 7132320, 14738400, 22866096, 23408640, 37748160, 46835712, 47486208, 58752000, 76658400, 79233024, 124416000, 174182400, 297198720

Offset

1,2

Comments

Odd terms are of the form Product_{0<=i<=m} F_i, 0<=m<=4, where F_i is a Fermat prime 2^(2^i)+1.

Contains also 1226400, 3456000, 14738400, 174182400, and 4294967295.

Links

Donovan Johnson, Table of n, a(n) for n = 1..41 (terms < 2^35)

Example

a(11) = 3*5*17*257.

Crossrefs

Cf. A047994.

Sequence in context: A120601 A145272 A264705 * A126453 A007081 A126455

Adjacent sequences: A117817 A117818 A117819 * A117821 A117822 A117823

Keyword

nonn

Author

Yasutoshi Kohmoto, Apr 30 2006

Status

approved