OFFSET
1,1
COMMENTS
Essentially the same as A036335.
What would be the ratio between a(n) and all possible numbers with n digits for each n?
EXAMPLE
a(1) = A006880(1) = 4.
MATHEMATICA
Table[Count[Range[10^(n-1), 10^n-1], _?(PrimeOmega[#]==n&)], {n, 8}] (* Harvey P. Dale, Apr 22 2011 *)
AlmostPrimePi[k_Integer, n_] := Module[{a, i}, a[0] = 1; If[k == 1, PrimePi[n], Sum[PrimePi[n/Times @@ Prime[Array[a, k - 1]]] - a[k - 1] + 1, Evaluate[ Sequence @@ Table[{a[i], a[i - 1], PrimePi[(n/Times @@ Prime[Array[a, i - 1]])^(1/(k - i + 1))]}, {i, k - 1}]]]]]; (* Eric W. Weisstein, Feb 07 2006 *)
f[n_] := AlmostPrimePi[n, 10^n - 1] - AlmostPrimePi[n, 10^(n - 1) - 1]; Array[f, 12] (* Robert G. Wilson v, Jul 06 2012 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
J. M. Bergot, Apr 08 2011
EXTENSIONS
Corrected and extended by Ray Chandler, Apr 11 2011
a(9)-a(12) from Ray Chandler, Apr 12 2011
a(13)-a(16) from Robert G. Wilson v, Jul 06 2012
STATUS
approved