A160725 - OEIS

%I #8 Jan 20 2019 23:16:47

%S 106,201,202,203,205,206,209,301,302,303,305,309,403,407,501,502,505,

%T 703,706,707,802,803,807,901,905,11013,11014,11015,11017,11019,11021,

%U 11023,11029,11031,11035,11038,11041,11042,11051,11053

%N Cyclops semiprimes.

%C Cyclops numbers (A134808) that are also semiprimes (A001358).

%H Robert Israel, <a href="/A160725/b160725.txt">Table of n, a(n) for n = 1..10000</a>

%p g:= proc(x,n)

%p   local L,i;

%p   L:= convert(x+9^(2*n),base,9);

%p   add((L[i]+1)*10^(i-1),i=1..n)+add((L[i]+1)*10^i,i=n+1..2*n)

%p end proc:

%p select(t -> numtheory:-bigomega(t)=2,[seq(seq(g(i,n),i=0..9^(2*n)-1),n=1..2)]); # _Robert Israel_, Jan 20 2019

%t Select[Range@ 12000, And[OddQ@ #2, #3[[Ceiling[#2/2] ]] == 0, Count[#3, 0] == 1, PrimeOmega@ #1 == 2] & @@ {#, IntegerLength@ #, IntegerDigits@ #} &] (* or *)

%t Select[Flatten@ Table[a (10^(d + 1)) + b, {d, 2}, {a, FromDigits /@ Tuples[Range@ 9, {d}]}, {b, FromDigits /@ Tuples[Range@ 9, {d}]}], PrimeOmega@ # == 2 &] (* _Michael De Vlieger_, Jan 20 2019 *)

%Y Cf. A001358, A134808, A134809, A138131, A138148, A153806, A153807, A160711, A160712, A160717.

%K easy,nonn,base

%O 1,1

%A _Omar E. Pol_, Jun 12 2009