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 A164914 a(n) = A164853(n+1)/A164853(n). 1

%I

%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

%Y Cf. A001358, A164853.

%K nonn

%O 1,1

%A _Zak Seidov_ and _Jonathan Vos Post_, Aug 31 2009

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Last modified August 7 11:08 EDT 2020. Contains 336275 sequences. (Running on oeis4.)