A103399 Semiprimes in A103379.

4, 9, 15, 21, 33, 38, 58, 65, 86, 106, 121, 129, 265, 511, 2047, 2049, 4097, 4109, 17855, 19857, 32663, 34709, 104739, 130393, 131889, 140474, 220918, 262978, 266174, 274759, 540933, 568083, 1312526, 1665242, 1833203, 2179101, 2295571

Offset: 1

Author

Jonathan Vos Post, Feb 15 2005

Keywords

• nonn

Examples

			A103379(21) = 4 = 2 * 2, which is semiprime, hence 4 is in this sequence.
		

Crossrefs

Cf. A001358, A103379, A103389.

Programs

Maple

isA103379 := proc(n)
    option remember ;
    local i ;
    for i from 1 do
        if A103379(i) = n then
            return true ;
        elif A103379(i) > n then
            return false ;
        fi;
    od:
end proc:
A103399 := proc(n)
    option remember ;
    local a, i ;
    if n = 1 then
        4;
    else
        for a from procname(n-1)+1 do
            if numtheory[bigomega](a) = 2 then
                if isA103379(a) then
                    return a ;
                fi;
            fi;
        end do:
    end if;
end proc:
for n from 1 do
    printf("%d,\n",A103399(n)) ;
end do: # R. J. Mathar, Aug 30 2008

Mathematica

SemiprimeQ[n_]:=Plus@@FactorInteger[n][[All, 2]]?2; Clear[a]; k11; Do[a[n]=1, {n, k+1}]; a[n_]:=a[n]=a[n-k]+a[n-k-1]; A103379=Array[a, 100] A103389=Union[Select[Array[a, 1000], PrimeQ]] A103399=Union[Select[Array[a, 300], SemiprimeQ]] N[Solve[x^12 - x - 1 == 0, x], 111][[2]] (* Program, edit and extension by Ray Chandler and Robert G. Wilson v *)

Formula

Intersection of A103379 and A001358.

Extensions

Corrected from a(15) on by R. J. Mathar, Aug 30 2008