cp's OEIS Frontend

A103399 Semiprimes in A103379.

%I A103399 #30 Sep 01 2024 02:37:56
%S A103399 4,9,15,21,33,38,58,65,86,106,121,129,265,511,2047,2049,4097,4109,
%T A103399 17855,19857,32663,34709,104739,130393,131889,140474,220918,262978,
%U A103399 266174,274759,540933,568083,1312526,1665242,1833203,2179101,2295571
%N A103399 Semiprimes in A103379.
%F A103399 Intersection of A103379 and A001358.
%e A103399 A103379(21) = 4 = 2 * 2, which is semiprime, hence 4 is in this sequence.
%p A103399 isA103379 := proc(n)
%p A103399     option remember ;
%p A103399     local i ;
%p A103399     for i from 1 do
%p A103399         if A103379(i) = n then
%p A103399             return true ;
%p A103399         elif A103379(i) > n then
%p A103399             return false ;
%p A103399         fi;
%p A103399     od:
%p A103399 end proc:
%p A103399 A103399 := proc(n)
%p A103399     option remember ;
%p A103399     local a, i ;
%p A103399     if n = 1 then
%p A103399         4;
%p A103399     else
%p A103399         for a from procname(n-1)+1 do
%p A103399             if numtheory[bigomega](a) = 2 then
%p A103399                 if isA103379(a) then
%p A103399                     return a ;
%p A103399                 fi;
%p A103399             fi;
%p A103399         end do:
%p A103399     end if;
%p A103399 end proc:
%p A103399 for n from 1 do
%p A103399     printf("%d,\n",A103399(n)) ;
%p A103399 end do: # _R. J. Mathar_, Aug 30 2008
%t A103399 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_ *)
%Y A103399 Cf. A001358, A103379, A103389.
%K A103399 nonn
%O A103399 1,1
%A A103399 _Jonathan Vos Post_, Feb 15 2005
%E A103399 Corrected from a(15) on by _R. J. Mathar_, Aug 30 2008