OFFSET
1,6
COMMENTS
LINKS
FORMULA
Dirichlet g.f.: primezeta(s)^2. - Benedict W. J. Irwin, Jul 11 2018
MATHEMATICA
Table[Total@ Map[Times @@ Boole@ {PrimeQ@ #, PrimeQ[n/#]} &, FactorInteger[n][[All, 1]]], {n, 95}] (* Michael De Vlieger, Jul 29 2017 *)
PROG
(PARI) a(n)=sumdiv(n, d, isprime(d)*isprime(n/d)) \\ Ralf Stephan, Oct 30 2013
(PARI) a(n) = my(f=factor(f)); (vecsum(f[, 2])==2) * #f~ \\ David A. Corneth, Jul 28 2017
(PARI) first(n) = my(v = vector(n)); forprime(p = 2, sqrtint(n), v[p^2] = 1; forprime(q = p + 1, n \ p, v[p*q] = 2)); v \\ David A. Corneth, Jul 28 2017
(Python)
from sympy import factorint
def A230595(n): return 0 if sum(f:=factorint(n).values())!=2 else len(f) # Chai Wah Wu, Jul 23 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Oct 27 2013
STATUS
approved