UPhi

[koh]

    Hi, Seqfans
    I posted a sequence related with a divisor function.
    

    %I A000001
    %S A000001 4,6,12,16,30,48,60,168,256,510,768,1020,3840,4080,14880,6528,65536

    %N A000001 Numbers such that 2*UnitaryPhi(2*UnitaryPhi(n))=n.
    %C A000001 Numbers of the form 2^(2^m), 1<=m<=5 exist on the sequence. 
               In other form, it is Product_{0<=i<=m} F_i + 1, 0<=m<=4, where F_i is Fermat prime 2^(2^i)+1  
    
    %Y A000001 A047994,A117820
    %K A000001 none
    %O A000001 1,1
    %A A000001 Yasutsohi Kohmoto   zbi74583 at boat.zero.ad,jp 
    


    Yasutoshi