Prime numbers which contain 123: Difference between revisions

=={{header|Nim}}==

<lang Nim>import sequtils, strutils

const N = 1_000_000 - 1 # Sieve of Erathostenes size.

# Sieve of Erathostenes.

var composite: array[2..N, bool]

for n in countup(3, N, 2): # We ignore the even values.

let n2 = n * n

if n2 > N: break

if not composite[n]:

for k in countup(n2, N, 2 * n):

composite[k] = true

template isPrime(n: Positive): bool = not composite[n]

iterator primes123(lim: Positive): int =

var n = 1001 # First odd value with four digits.

while n <= lim:

if n.isPrime and ($n).find("123") >= 0:

yield n

inc n, 2

let list = toSeq(primes123(100_000 - 1))

echo "Found ", list.len, " “123” primes less than 100_000:"

for i, n in list:

stdout.write ($n).align(5), if (i + 1) mod 8 == 0: '\n' else: ' '

echo '\n'

var count = 0

for _ in primes123(1_000_000): inc count

echo "Found ", count, " “123” primes less than 1_000_000."</lang>

{{out}}

<pre>Found 46 “123” primes less than 100_000:

1123 1231 1237 8123 11239 12301 12323 12329

12343 12347 12373 12377 12379 12391 17123 20123

22123 28123 29123 31123 31231 31237 34123 37123

40123 41231 41233 44123 47123 49123 50123 51239

56123 59123 61231 64123 65123 70123 71233 71237

76123 81233 81239 89123 91237 98123

Found 451 “123” primes less than 1_000_000.</pre>