generate_numbers_with_given_edges.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 28 July 2021
# https://github.com/trizen

# Generate numbers that begin and end with a given list of digits.

# See also:
#   https://rosettacode.org/wiki/Primes_whose_first_and_last_number_is_3

func numbers_with_edges(upto, base = 10, s = [3]) {
    Enumerator({|callback|
        callback(s.digits2num(base))
        for k in (0 .. base**(upto.len(base) - 2*s.len)) {

            break if (s + k.digits(base) + s -> digits2num(base) > upto)

            Inf.times { |j|

                var d = (s + k.digits(base) + j.of(0) + s)
                var n = d.digits2num(base)

                (n <= upto) ? callback(n) : break
            }
        }
    })
}

# Example for numbers which begin and end in 3

with (1e4) { |n|
    var list = numbers_with_edges(n).to_a.sort
    say "There are #{list.len} integers <= #{n.commify} which begin and end in 3:"
    list.each_slice(10, {|*a| say a.map { '%5s' % _ }.join(' ') })

    list.grep! { .is_prime }

    say "\nThere are #{list.len} primes <= #{n.commify} which begin and end in 3:"
    list.each_slice(10, {|*a| say a.map { '%5s' % _ }.join(' ') })
}

__END__
There are 111 integers <= 10,000 which begin and end in 3:
    3   303   313   323   333   343   353   363   373   383
  393  3003  3013  3023  3033  3043  3053  3063  3073  3083
 3093  3103  3113  3123  3133  3143  3153  3163  3173  3183
 3193  3203  3213  3223  3233  3243  3253  3263  3273  3283
 3293  3303  3313  3323  3333  3343  3353  3363  3373  3383
 3393  3403  3413  3423  3433  3443  3453  3463  3473  3483
 3493  3503  3513  3523  3533  3543  3553  3563  3573  3583
 3593  3603  3613  3623  3633  3643  3653  3663  3673  3683
 3693  3703  3713  3723  3733  3743  3753  3763  3773  3783
 3793  3803  3813  3823  3833  3843  3853  3863  3873  3883
 3893  3903  3913  3923  3933  3943  3953  3963  3973  3983
 3993

There are 33 primes <= 10,000 which begin and end in 3:
    3   313   353   373   383  3023  3083  3163  3203  3253
 3313  3323  3343  3373  3413  3433  3463  3533  3583  3593
 3613  3623  3643  3673  3733  3793  3803  3823  3833  3853
 3863  3923  3943