public static IEnumerable <long> Get()
{
var pandigitals =
SetUtils.Permutations(Enumerable.Range(0, 10).Select(x => (long)x))
.Select(d => d.Reverse())
.Where(digits => digits.First() != 0);
return(pandigitals.Where(HasSubstringDivisibility).Select(x => x.DigitsToNumber()));
}
public static IEnumerable <string> Main()
{
var fourDigitPrimes = new HashSet <long>(PrimeUtils.Primes
.SkipWhile(x => x.ToString().Length < 4)
.TakeWhile(x => x.ToString().Length == 4));
while (fourDigitPrimes.Any())
{
var prime = fourDigitPrimes.First();
var permutations = SetUtils.Permutations(MiscUtils.GetDigits(prime)).Select(x => (long)x.DigitsToNumber()).Where(x => x > 1000);
var primePermutations = fourDigitPrimes.Intersect(permutations).ToArray();
if (primePermutations.Length >= 3)
{
var threes = primePermutations.Choose(3).ToArray();
foreach (var special in threes.Where(HaveEqualDifference))
{
yield return(string.Join("", special.OrderBy(x => x)));
}
}
fourDigitPrimes.ExceptWith(primePermutations);
}
}
public static IEnumerable <int[]> PandigitalNumbers(int pandigital)
{
return(SetUtils.Permutations(Enumerable.Range(1, pandigital)));
}