what is the value "60" doing in A000028 ??

Meeussen Wouter (bkarnd) wouter.meeussen at vandemoortele.com
Tue Sep 11 17:50:57 CEST 2001

same for "84" = 2 * 42 , and others.

Also remark that 76 does not appear in either sequence A000028 or A000379
and since it's 4*19 it belongs to A000379.

There is however a quite different construction that generates A000028 and
as they stand (with the lost "76" added). That one is based on the MoebiusMu
-analog for infinitary divisors, defined by forcing mu() into the role of
MoebiusMu :
    the sum over the i-divisors of the function mu(n/i_d)*s[i_d] should
    the sum over the i-divisors of s[i_d]. Solve for mu().

Q: was the Name " a(n) is smallest number not of form a(i)a(j), i<j<n."
   added at a later date? 

***********  in plain 'Hungarian', this 'different construction' is


iDivisors[k_Integer]:= (Times @@ (First[it]^(#1 /. z -> List)) & ) /@ 
   Flatten[Outer[z,Sequence @@ bitty/@Last[it=Transpose[FactorInteger[k]]],
1]] ;

SumOveriDivisors[f_,n_Integer]:=Plus@@(Map[f[#1,n]&,  iDivisors[n]  ]);
inverseimoebius[seq_]:=SumOveriDivisors[ seq[[#1]]  &, # ]& /@

seq= s/@ Range[0, 632] ;
itry=SumOveriDivisors[\[Mu][#2/#1] seq[[#1]]  &, # ]& /@ Range[Length[seq]]

Array[\[Mu],632]/.Solve[Thread[inv== Array[s,633,0]   ],  Array[\[Mu],633]

the positions of "1" are A000028 and those of "-1" are A000379 (or the other
way 'round).

Wouter Meeussen
tel  +32 (0)51 332 124
fax +32 (0)51 332 175
mail: wouter.meeussen at vandemoortele.com

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