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%I #12 Feb 02 2015 11:04:07
%S 2,1,2,2,1,0,2,2,2,2,4,4,3,3,2,2,3,2,1,2,2,1,5,4,4,3,4,3,3,2,2,2,2,1,
%T 3,1,2,2,1,2,2,1,6,5,5,4,4,3,5,5,3,3,2,5,4,4,4,4,2,3,2,5,4,4,3,3,3,4,
%U 3,3,2,3,3,2,2,4,2,2,1,2,1,1,6,6,6,5,6,5,3,6,5,4,5,4,4,4,3,5,4,4,2,6,5,5,4
%N Number of 0's in binary representation of n-th semiprime.
%F a(n) = A023416(A001358(n)). - _R. J. Mathar_, May 23 2010
%e a(1)=2 because 1st semiprime = 4 = 100_2.
%e a(2)=1 because 2nd semiprime = 6 = 110_2.
%p A023416 := proc(n) a := 0 ; for d in convert(n,base,2) do if d = 0 then a := a+1 ; end if; end do; a ; end proc:
%p A178064 := proc(n) A023416(A001358(n)) ; end proc:
%p seq(A178064(n),n=1..120) ; # _R. J. Mathar_, May 23 2010
%t DigitCount[#, 2, 0] & /@ Select[Range@ 328, PrimeOmega@ # == 2 &] (* _Michael De Vlieger_, Feb 02 2015 *)
%Y Cf. A001358, A035103.
%K nonn
%O 1,1
%A _Juri-Stepan Gerasimov_, May 18 2010
%E a(56) corrected by _R. J. Mathar_, May 23 2010
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