This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A178064 #12 Feb 02 2015 11:04:07 %S A178064 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 A178064 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 A178064 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 A178064 Number of 0's in binary representation of n-th semiprime. %F A178064 a(n) = A023416(A001358(n)). - _R. J. Mathar_, May 23 2010 %e A178064 a(1)=2 because 1st semiprime = 4 = 100_2. %e A178064 a(2)=1 because 2nd semiprime = 6 = 110_2. %p A178064 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 A178064 := proc(n) A023416(A001358(n)) ; end proc: %p A178064 seq(A178064(n),n=1..120) ; # _R. J. Mathar_, May 23 2010 %t A178064 DigitCount[#, 2, 0] & /@ Select[Range@ 328, PrimeOmega@ # == 2 &] (* _Michael De Vlieger_, Feb 02 2015 *) %Y A178064 Cf. A001358, A035103. %K A178064 nonn %O A178064 1,1 %A A178064 _Juri-Stepan Gerasimov_, May 18 2010 %E A178064 a(56) corrected by _R. J. Mathar_, May 23 2010