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%I #21 Sep 20 2021 04:58:29
%S 1,1,2,6,6,30,180,1260,1260,1260,12600,138600,138600,1801800,25225200,
%T 378378000,378378000,6432426000,6432426000,122216094000,122216094000,
%U 2566537974000,56463835428000,1298668214844000,1298668214844000,1298668214844000,33765373585944000
%N Product of squarefree numbers less than n+1.
%H G. C. Greubel, <a href="/A179215/b179215.txt">Table of n, a(n) for n = 0..680</a>
%F a(n) = Product_{k=1..n} k^A008966(k).
%F A001221(a(n)) = A000720(n).
%F Subsequence of A025487.
%F A034386(n) <= a(n) <= A000142(n).
%F A179214(n) = a(2*n)/a(n-1) for n>0.
%p a:= proc(n) option remember; `if`(n=0, 1,
%p a(n-1)*`if`(issqrfree(n), n, 1))
%p end:
%p seq(a(n), n=0..27); # _Alois P. Heinz_, Sep 20 2021
%t With[{sfnos=Select[Range[50],SquareFreeQ]},Table[Times@@Select[sfnos, #<n+1&],{n,0,30}]] (* _Harvey P. Dale_, Jun 13 2011 *)
%o (PARI) a(n) = prod(k=1, n, if (issquarefree(k), k, 1)); \\ _Michel Marcus_, Sep 20 2021
%o (PARI) a(n) = my(p=1); forsquarefree(x=1, n, p*=x[1]); p; \\ _Michel Marcus_, Sep 20 2021
%Y Cf. A013928, A066779, A005117, A008966, A179214.
%Y Cf. A000142, A000720, A001221, A025487, A034386.
%K nonn
%O 0,3
%A _Reinhard Zumkeller_, Jul 05 2010
%E Definition corrected by _Harvey P. Dale_, Jun 13 2011
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