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A111939
Number of primes < semiprime(n).
2
2, 3, 4, 4, 6, 6, 8, 8, 9, 9, 11, 11, 11, 12, 12, 14, 15, 15, 16, 16, 16, 18, 18, 19, 21, 21, 22, 23, 23, 23, 24, 24, 24, 24, 27, 29, 30, 30, 30, 30, 30, 30, 31, 32, 32, 34, 34, 34, 34, 34, 36, 37, 37, 37, 38, 39, 40, 40, 42, 42, 42, 44, 46, 46, 46, 46, 46, 46, 47, 47, 47, 47, 47
OFFSET
1,1
LINKS
FORMULA
a(n) = A000720(A001358(n)).
MATHEMATICA
PrimePi@Select[Range@218, Plus @@ Last /@ FactorInteger@# == 2 &] (* Robert G. Wilson v, Jan 10 2006 *)
PrimePi/@Select[Range[300], PrimeOmega[#]==2&] (* Harvey P. Dale, Nov 16 2014 *)
CROSSREFS
Partial sums of A176451.
Sequence in context: A304575 A296421 A138768 * A253248 A341112 A329004
KEYWORD
nonn
AUTHOR
Giovanni Teofilatto, Nov 27 2005
EXTENSIONS
More terms from Robert G. Wilson v, Lambert Herrgesell (zero815(AT)googlemail.com) and Matthew Conroy, Dec 16 2005
Entry revised by Ray Chandler, Sep 20 2006
STATUS
approved