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

3, 15, 120, 1080, 14040, 196560, 3931200, 82555200, 1981324800, 49533120000, 1585059840000, 52306974720000, 1778437140480000, 65802174197760000, 2500482619514880000, 112521717878169600000, 5401042458152140800000

Offset: 1

Author

Jonathan Vos Post, Nov 28 2005

Keywords

• easy
• nonn

Comments

Semiprime analog of A005867.

Examples

			a(10) = 3*5*8*9*13*14*20*21*24*25 =
(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).
		

Crossrefs

Cf. A001358, A005867.

Programs

Mathematica

FoldList[Times,Select[Range[50],PrimeOmega[#]==2&]-1] (* Harvey P. Dale, Jan 21 2023 *)

PARI

A001358(n)={
    if(n==1,
        return(4),
        for(a=A001358(n-1)+1,100000000000000000,
            if (bigomega(a)==2,
                return(a)
            ) ;
        ) ;
    ) ;
}
A112228(n)={
    prod(i=1,n,A001358(i)-1)
} /* R. J. Mathar, Mar 09 2012 */

Formula

a(n) = Prod[from i = 1 to n] (A001358(i)-1).