OFFSET
1,2
COMMENTS
Might be roughly n^2/2 (seems to be marginally more at least for small n).
LINKS
Michel Marcus, Table of n, a(n) for n = 1..5000
FORMULA
a(n) = pi(n*prime(n)).
EXAMPLE
a(4)=9 since 4th prime is 7, 4*7=28, greatest prime less than or equal to 28 is 23 which is the 9th prime.
MAPLE
a:= n-> numtheory[pi](n*ithprime(n)):
seq(a(n), n=1..61); # Alois P. Heinz, Aug 30 2019
MATHEMATICA
Table[PrimePi[w*Prime[w]], {w, 1, 100}]
PROG
(PARI) a(n) = primepi(n*prime(n)); \\ Michel Marcus, Aug 30 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Henry Bottomley, Nov 13 2000
STATUS
approved