A178064 Number of 0's in binary representation of n-th semiprime.

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, 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, 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

Offset: 1

Author

Juri-Stepan Gerasimov, May 18 2010

Keywords

• nonn

Examples

			a(1)=2 because 1st semiprime = 4 = 100_2.
a(2)=1 because 2nd semiprime = 6 = 110_2.
		

Crossrefs

Cf. A001358, A035103.

Programs

Maple

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:
A178064 := proc(n) A023416(A001358(n)) ; end proc:
seq(A178064(n),n=1..120) ; # R. J. Mathar, May 23 2010

Mathematica

DigitCount[#, 2, 0] & /@ Select[Range@ 328, PrimeOmega@ # == 2 &] (* Michael De Vlieger, Feb 02 2015 *)

Formula

a(n) = A023416(A001358(n)). - R. J. Mathar, May 23 2010

Extensions

a(56) corrected by R. J. Mathar, May 23 2010