var factorial_primes = Enumerator({|f|
    for k in (1..Inf) {
        if (k!-1 -> is_prime) { f([k, -1]) }
        if (k!+1 -> is_prime) { f([k, +1]) }
    }
})

func abr(v) {
    v.len <= 40 ? v : (v.to_s.first(20) + '..' + v.to_s.last(20) + " (#{v.len} digits)")
}

factorial_primes.first(30).each_2d {|k,i|
    printf("%3d! %s %d = %s\n", k, (i.sgn < 0 ? '-' : '+'), i.abs, abr(k! + i))
}