Meissel's Formula
A modification of Legendre's formula for the prime counting function
. It starts with
where
is the floor function,
is the number of integers
with
, and
is the number of integers
with
, and so on.
Identities satisfied by the
s include
![P_2(x,a)=sum[pi(x/(p_i))-(i-1)]](https://mathworld.wolfram.com/images/equations/MeisselsFormula/NumberedEquation1.gif) |
(2)
|
for
and
Meissel's formula is
 |
(5)
|
where
Taking the derivation one step further yields Lehmer's formula.
REFERENCES:
Gram, J. "Rapport sur quelques calculs entrepris par M. Bertelsen et concernant les nombres premiers." Acta Math. 17, 301-314, 1893.
Hardy, G. H. Ramanujan: Twelve Lectures on Subjects Suggested by His Life and Work, 3rd ed. New York: Chelsea, p. 46, 1999.
Mathews, G. B. Ch. 10 in Theory of Numbers. New York: Chelsea, 1961.
Meissel, E. D. F. "Berechnung der Menge von Primzahlen, welche innerhalb der ersten Milliarde naturlicher Zahlen vorkommen." Math. Ann. 25, 251-257, 1885.
Riesel, H. "Meissel's Formula." Prime Numbers and Computer Methods for Factorization, 2nd ed. Boston, MA: Birkhäuser, pp. 12-13, 1994.
Séroul, R. "Meissel's Formula." §8.7.3 in Programming for Mathematicians. Berlin: Springer-Verlag, pp. 179-181, 2000.