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Semiprimes n such that n+1 and n+2 are squarefree.
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%I #11 May 15 2020 02:26:57

%S 4,9,21,33,57,65,69,77,85,93,121,129,141,177,185,201,209,213,217,221,

%T 237,253,265,289,301,309,321,329,365,381,393,417,437,445,453,469,481,

%U 497,501,517,533,545,553,581,589,597,633,669,681,689,697,713,717,753

%N Semiprimes n such that n+1 and n+2 are squarefree.

%C Terms computed by _Zak Seidov_.

%C Except 4, all terms == 1 (mod 4). - _Robert Israel_, May 14 2020

%H Robert Israel, <a href="/A146948/b146948.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= n -> numtheory:-bigomega(n)=2 and numtheory:-issqrfree(n+1) and numtheory:-issqrfree(n+2):

%p select(filter, [4,seq(i,i=5..1000,4)]); # _Robert Israel_, May 14 2020

%t Select[Range[800],PrimeOmega[#]==2&&And@@SquareFreeQ/@(#+{1,2})&] (* _Harvey P. Dale_, Oct 30 2013 *)

%K nonn,less

%O 1,1

%A _Giovanni Teofilatto_, Nov 03 2008