prog.sf

#!/usr/bin/ruby

# Number of odd semiprimes less than 2^n.
# https://oeis.org/A362042

# Terms:
#   0, 0, 0, 0, 2, 4, 11, 24, 51, 103, 207, 417, 815, 1622, 3164, 6210, 12146, 23711, 46295, 90307, 176369, 344155, 672091, 1312721, 2565048, 5013566, 9804910, 19183069, 37547164, 73526846, 144042323, 282317826, 553564500, 1085869406, 2130916524, 4183381508, 8215884036, 16141427963, 31723866361, 62370738996, 122665338058, 241325794755, 474921367858, 934913584263, 1840977104092, 3626171491221, 7144421771451, 14079941975945, 27755296183385, 54726597576934, 107933230558886, 212918183021710, 420114808112636, 829120908511644, 1636663786905232, 3231394736936333, 6381265628131569, 12603969451816191, 24899413334814548, 49198265137944157, 97227049414548237, 192175889896107844, 379912070399250915, 751169045016870577

func odd_semiprime_count(n) is cached {
    n.semiprime_count - idiv(n,2).pi
}

with (1e6.irand) {|n|
    assert_eq(
        n.semiprimes.count{.is_odd},
        odd_semiprime_count(n)
    )
}

for n in (0 .. 1e6) {
    print(odd_semiprime_count(2**n), ", ")
}