the number of primes between factorial(n) and factorial(2n).sf

#!/usr/bin/ruby
# https://oeis.org/A076960

# Number of primes <= n!.
# https://oeis.org/A003604

# a(n) = A003604(2*n) - A003604(n). - ~~~~

# 58893601709293849, 23688535118130027712

# a(10)-a(11) from ~~~~ [based on data from A003604]

var a = [   0, 0, 1, 3, 9, 30, 128, 675, 4231, 30969, 258689, 2428956, 25306287, 289620751, 3610490805, 48686912930, 706003798139, 10953617995740, 181035032207760, 3175094503778521, 58893601709552538, 1151825702178908788, 23688535118132456668, 511050155316058710033]

for i in (0 .. a.len>>1) {
    say ("a(#{i}) = ", a[2*i]-a[i])
}