OFFSET
1,1
COMMENTS
These are the prime terms in A055729.
MATHEMATICA
Select[ Table[ PrimePi[ 3^n], {n, 0, 49}], PrimeQ@# &] (* Robert G. Wilson v, Feb 25 2010 *)
PROG
(PARI) primeslessxn2(n, p) = /*primes < p^n if prime */ { sr=0; for(x=0, n, y=primepi(p^x); if(y<>0, sr+=1.0/y); if(isprime(y), print1(y", ")); ); print(); print(sr) }
(Python)
from itertools import islice
from sympy import isprime, primepi
def A087865_gen(): # generator of terms
k = 1
while True:
k *= 3
if isprime(p:=primepi(k)):
yield p
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Cino Hilliard, Oct 27 2003
EXTENSIONS
a(6) added by David Baugh, Mar 17 2015
STATUS
approved