“I've got a few ideas," (Amy) admitted. "But I don't know where we're going in the long term. I mean - have you ever thought about what this ultimate treasure could be?""Something cool." (Dan)"Oh, that's real helpful. I mean, what could make somebody the most powerful Cahill in history? And why thirty-nine clues?"Dan shrugged. "Thirty-nine is a sweet number. It's thirteen times three. It's also the sum of five prime numbers in a row - 3,5,7,11,13. And if you add the first three powers of three, 3 to the first, 3 to the second, and s to the third, you get thirty-nine."Amy stared at him. "How did you know that?""What do you mean? It's obvious.”

“When you are five, you know your age down to the month. Even in your twenties, you know how old you are. I'm twenty-three you say, or maybe twenty-seven. But then in your thirties, something strange starts to happen. It is a mere hiccup at first, an instant of hesitation. How old are you? Oh, I'm--you start confidently, but then you stop. You were going to say thirty-three, but you are not. You're thirty-five. And then you're bothered, because you wonder if this is the beginning of the end. It is, of course, but it's decades before you admit it.”

“You should climb around inside my brain, Dan. It's like this dark room surrounded by quicksand.""I know what you mean," her brother said quietly. "I hate being in my brain sometimes. I have to get out.""What do you do?" Amy asked.Dan shrugged "I go to other places. My toes. My shoulders. But mostly here." He tapped his chest and immediately reddened. "I know. It's stupid.""Not really," Amy said. "I wish I could do that, too.”

“Thirty three thousand, three hundred and thirty three things. That’s all I need to get by. Oh, and I guess I also need love. Better make that thirty three thousand, three hundred and thirty four.”

“In your thirties something strange starts to happen. It’s a mere hiccup at first, an instant of hesitation. How old are you? Oh, I’m — you start confidently, but then you stop. You were going to say thirty-three, but you’re not. You’re thirty-five. And then you’re bothered, because you wonder if this is the beginning of the end. It is, of course, but it’s decades before you admit it.”

“Oh, we're very careful, Marilla. And it's so interesting. Two flashes means, "Are you there?" Three means "yes" and four "no." Five means, "Come over as soon as possible, because I have something important to reveal." Diana has just signalled five flashes, and I'm really suffering to know what it is.”