A103400 - OEIS

%I #25 Sep 01 2024 02:33:21

%S 4,9,15,21,33,38,58,65,86,106,121,129,265,511,2047,2049,4097,4109,

%T 8193,17855,19857,34709,66233,104739,130953,131209,140474,220918,

%U 258931,511673,540951

%N Semiprimes in A103380.

%F Intersection of A103380 and A001358.

%p A103380 := proc(n) option remember ; if n <= 13 then 1; else procname(n-12)+procname(n-13) ; fi; end: isA103380 := proc(n) option remember ; local i ; for i from 1 do if A103380(i) = n then RETURN(true) ; elif A103380(i) > n then RETURN(false) ; fi; od: end: A103400 := 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 isA103380(a) then RETURN(a) ; fi; fi; od: fi; end: for n from 1 to 37 do printf("%d, ",A103400(n)) ; od: # _R. J. Mathar_, Aug 30 2008

%t SemiprimeQ[n_]:=Plus@@FactorInteger[n][[All, 2]]?2; Clear[a]; k12; 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 Cf. A001358, A103380.

%K easy,nonn

%O 1,1

%A _Jonathan Vos Post_, Feb 16 2005

%E Corrected from a(15) on by _R. J. Mathar_, Aug 30 2008