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A136048 Semiprime terms in A136047. 3

%I #4 Oct 11 2015 10:33:09

%S 185,497,511,1041,1059,1903,3107,4705,4735,6817,9481,12761,16721,

%T 33379,48961,49027,68857,80561,80639,93521,179503,201241,250097,

%U 306281,306403,405551,482161,482303,523921,885631,947939,1081001,1081187,1226177

%N Semiprime terms in A136047.

%C 185 = 5*37, 497 = 7*71, 511 = 7*73, 1041 = 3*347, 1059 = 3*353, 1903 = 11*173, 3107 = 13*239, 4705 = 5*941, 4735 = 5*947, 6817 = 17*401, 9481 = 19*499, 12761 = 7*1823, 16721 = 23*727, 33379 = 29*1151, 48961 = 11*4451, 49027 = 11*4457, 68857 = 37*1861, 80561 = 13*6197, 80639 = 13*6203, 93521 = 41*2281.

%C Positions of a(n) in A136047 are given in A135439.

%t a[1]=1;a[n_]:=a[n]=a[n-1]+n^(1+Mod[n,2]);A136047=Table[a[n],{n,1000}]; A136048=Select[A136047,Total[Last/@FactorInteger[ # ]]==2&]

%t nxt[{n_,a_}]:={n+1,If[OddQ[n],a+n+1,a+(n+1)^2]}; Select[ Transpose[ NestList[ nxt,{1,1},200]][[2]],PrimeOmega[#]==2&] (* _Harvey P. Dale_, Oct 11 2015 *)

%Y Cf. A136047.

%K nonn

%O 1,1

%A _Zak Seidov_, Dec 12 2007

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Last modified March 28 04:05 EDT 2024. Contains 371235 sequences. (Running on oeis4.)