Problem 17: If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?

After simplifying, and taking care to spell “forty” correctly.

let problem17d =
    "OneThousand".Length +
    
    "OneHundred".Length +
    "TwoHundred".Length +
    "ThreeHundred".Length +
    "FourHundred".Length +
    "FiveHundred".Length +
    "SixHundred".Length +
    "SevenHundred".Length +
    "EightHundred".Length +
    "NineHundred".Length +
    
    99*("OneHundredAnd".Length +
        "TwoHundredAnd".Length +
        "ThreeHundredAnd".Length +
        "FourHundredAnd".Length +
        "FiveHundredAnd".Length +
        "SixHundredAnd".Length +
        "SevenHundredAnd".Length +
        "EightHundredAnd".Length +
        "NineHundredAnd".Length) +
    
    10*("OneTwoThreeFourFiveSixSevenEightNineTenElevenTwelveThirteenFourteenFifteenSixteenSeventeenEighteenNineteen".Length +
        10*("Twenty".Length + "Thirty".Length + "Forty".Length + "Fifty".Length + "Sixty".Length + "Seventy".Length + "Eighty".Length + "Ninety".Length) +
        8*("OneTwoThreeFourFiveSixSevenEightNine".Length))