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%I #15 Aug 28 2020 08:10:56
%S 3,3,5,7,1,1,11,5,13,1,17,1,19,1,23,7,1,1,1,29,31,1,1,37,1,41,1,43,1,
%T 1,1,47,1,53,1,1,59,1,11,61,1,1,1,67,1,71,1,1,73,1,79,1,1,83,13,1,89,
%U 1,1,1,97,1,101,1,1,103,1,1,107,1,1,109,1,1,113,1,1,1,1,1,127,1,131,1,1,137
%N a(n) = A164853(n+1)/A164853(n).
%C Or, lcm(first n+1 semiprimes) / lcm(first n semiprimes).
%C All terms are 1 or prime.
%C a(n) = p if A001358(n+1) is 2*p or p^2 where p is prime, otherwise a(n)=1. - _Robert Israel_, May 31 2018
%H Robert Israel, <a href="/A164914/b164914.txt">Table of n, a(n) for n = 1..10000</a>
%p N:= 1000: # to use the semiprimes <= N
%p P:= select(isprime, [2,seq(i,i=3..N/2,2)]):
%p S:= sort(convert({seq(op(p*select(`<=`,P,N/p)),p=P)},list)):
%p map(proc(t) if issqr(t) then sqrt(t) elif t::even then t/2 else 1 fi end proc, S[2..-1]); # _Robert Israel_, May 31 2018
%t A164853 = With[{s = Select[Range[1000], PrimeOmega[#] == 2&]}, Table[LCM @@ Take[s, n], {n, Length[s]}]];
%t Rest@A164853 / Most@A164853 (* _Jean-François Alcover_, Aug 28 2020, after _Harvey P. Dale_ in A164853 *)
%Y Cf. A001358, A164853.
%K nonn
%O 1,1
%A _Zak Seidov_ and _Jonathan Vos Post_, Aug 31 2009
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