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%I #6 Jun 02 2016 12:53:44
%S 1,1,1,1,2,1,1,7,3,1,3,8,5,13,8,14,9,9,9,19,13,9,15,16,15,28,10,29,17,
%T 17,21,38,24,25,19,25,43,44,20,29,49,31,1,37,31,38,35,58,29,37,67,41,
%U 68,51,8,47,77,49,46,58,49,7,82,51,59,47,51,83,11,53,66,92
%N Write the n-th squarefree semiprime as prime(m)*prime(k). Then a(n) is the absolute value of prime(m)*k-prime(k)*m.
%e a(1)=1 because prime(1)*2-prime(2)*1=4-3=1; a(2)=1 because prime(1)*3-prime(3)*2=6-5=1.
%p A006881 := proc(n)
%p option remember;
%p if n = 1 then
%p 6;
%p else
%p for a from procname(n-1)+1 do
%p if numtheory[bigomega](a)=2 and issqrfree(a) then
%p return a;
%p end if;
%p end do:
%p end if;
%p end proc:
%p A169730 := proc(n)
%p local p,k,pm,pk;
%p p := numtheory[factorset](A006881(n)) ;
%p pm := op(1,p) ;
%p pk := op(2,p) ;
%p k := numtheory[pi](pk) ;
%p m := numtheory[pi](pm) ;
%p abs(pm*k-pk*m) ;
%p end proc:
%p seq(A169730(n),n=1..72) ; # _R. J. Mathar_, Jun 02 2016
%Y Cf. A006881.
%K nonn,less
%O 1,5
%A _Juri-Stepan Gerasimov_, Apr 28 2010
%E Corrected by _R. J. Mathar_, Jun 02 2016
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