A178064 - OEIS

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

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..105.

FORMULA

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

EXAMPLE

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

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

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: