UPhi

[koh]

    Hi, Seqfans
    I posted a sequence related with a divisor function.
    
    I think the odd solutions are beutiful.

    %I A000001
    %S A000001 1,3,15,216,255,1728,65535,182880,1226400,3456000,14738400,174182400,4294967295,

    %N A000001 Numbers such that UnitaryPhi(2*UnitaryPhi(n))=n.
    %C A000001 Odd terms are of the form Product_{0<=i<=m} F_i, 0<=m<=4, where F_i is Fermat prime 2^(2^i)+1  
    %e A000001   a(7)=3*5*17*257
    
    %Y A000001 A047994
    %K A000001 none
    %O A000001 1,2
    %A A000001 Yasutsohi Kohmoto   zbi74583 at boat.zero.ad,jp 
    
    I wonder if odd terms are all.

    Yasutoshi