OFFSET
0,2
FORMULA
a(n) = pi(10^n)/10^(n-2) rounded.
EXAMPLE
There are 4 primes less than 10 (i.e., 2, 3, 5, 7), so a(1) = 40.
MATHEMATICA
a[n_] := PrimePi[10^n]/10^(n-2) // Round;
(* or *) a[n_] := A006880[[n+1]]/10^(n-2) // Round; Table[Print["10^", n, " ", a[n], "%"]; a[n], {n, 0, 25}] (* Jean-François Alcover, Sep 27 2013 *)
CROSSREFS
KEYWORD
nonn,base,hard,less
AUTHOR
Jean-François Alcover, Sep 27 2013
STATUS
approved