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A112228 Product of the first n (semiprimes - 1).

%I A112228 #11 Jan 21 2023 13:17:44
%S A112228 3,15,120,1080,14040,196560,3931200,82555200,1981324800,49533120000,
%T A112228 1585059840000,52306974720000,1778437140480000,65802174197760000,
%U A112228 2500482619514880000,112521717878169600000,5401042458152140800000
%N A112228 Product of the first n (semiprimes - 1).
%C A112228 Semiprime analog of A005867.
%F A112228 a(n) = Prod[from i = 1 to n] (A001358(i)-1).
%e A112228 a(10) = 3*5*8*9*13*14*20*21*24*25 =
%e A112228 (4-1)*(6-1)*(9-1)*(10-1)*(14-1)*(15-1)*(21-1)*(22-1)*(25-1)*(26-1) = 49533120000, the product of the first 10 (semiprimes minus one).
%t A112228 FoldList[Times,Select[Range[50],PrimeOmega[#]==2&]-1] (* _Harvey P. Dale_, Jan 21 2023 *)
%o A112228 (PARI) A001358(n)={
%o A112228     if(n==1,
%o A112228         return(4),
%o A112228         for(a=A001358(n-1)+1,100000000000000000,
%o A112228             if (bigomega(a)==2,
%o A112228                 return(a)
%o A112228             ) ;
%o A112228         ) ;
%o A112228     ) ;
%o A112228 }
%o A112228 A112228(n)={
%o A112228     prod(i=1,n,A001358(i)-1)
%o A112228 } /* R. J. Mathar, Mar 09 2012 */
%Y A112228 Cf. A001358, A005867.
%K A112228 easy,nonn
%O A112228 1,1
%A A112228 _Jonathan Vos Post_, Nov 28 2005