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%I #10 Apr 14 2022 10:40:32
%S 4,9,21,46,93,187,377,755,1513,3027,6059,12127,24257,48529,97059,
%T 194127,388257,776515,1553033,3106083,6212177,12424355,24848723,
%U 49697447,99394909,198789819,397579639,795159283,1590318573,3180637153
%N a(1) = 4; a(n) is smallest semiprime > 2*a(n-1).
%C a(1)=4, a(n)=2*a(n-1)+k, where k is least positive integer chosen so that a(n) is the product of two primes. Corresponding k's are 1, 3, 4, 1, 1, 3, 1, 3, 1, 5, 9, 3, 15, 1, 9, 3, 1, 3, 17, 11, 1, 13, 1, 15, 1, 1, 5, 7, 7, 11, 5, 5, 15, 1, 3, 9, 9, 5, 7, 8, ... - _Zak Seidov_, Dec 24 2007
%e a(1)=4, then
%e k=1, a(2)=2*4+1=9,
%e k=3, a(3)=2*9+3=21,
%e k=4, a(4)=2*21+4=46,
%e k=1, a(5)=2*46+1=93,
%e k=1, a(6)=2*93+1=187.
%t a=4;Do[Do[b=2a+n;If[2==Plus@@FactorInteger[b][[All,2]],Print[{b,n}];Break[]],{n,1000}];a=b,{40}] - _Zak Seidov_, Dec 24 2007
%t ssp[n_]:=Module[{k=2n+1},While[PrimeOmega[k]!=2,k++];k]; NestList[ssp,4,30] (* _Harvey P. Dale_, Apr 14 2022 *)
%Y Semiprime analog of A055496.
%Y Cf. A001358, A076656.
%K easy,nonn,less
%O 1,1
%A _Jonathan Vos Post_, May 04 2006
%E Edited by _N. J. A. Sloane_, Jul 01 2008 at the suggestion of _R. J. Mathar_