public static long Solution()
{
int prime = 7;
long solution = 0;
var limits = UtilityFunctions.Digits(limit - 1, prime);
var numberOfDigits = limits.Count;
var defaultLimit = prime * (prime + 1) / 2;
for (int index = 0; index <= numberOfDigits; index++)
{
long thisFactor = 1;
for (int j = numberOfDigits - 1; j >= 0; j--)
{
if (j < index)
{
thisFactor *= limits[numberOfDigits - j - 1] + 1;
}
else if (j == index)
{
thisFactor *= limits[numberOfDigits - j - 1] * (limits[numberOfDigits - j - 1] + 1) / 2;
}
else
{
thisFactor *= defaultLimit;
}
}
solution += thisFactor;
}
return(solution);
}