I'd bet it's more the "7" effect. When asked to pick a number between 1 and 10, 7 is picked more often than other numbers. Someone below mentioned that magician

I'd bet it's more the "7" effect. When asked to pick a number between 1 and 10, 7 is picked more often than other numbers. Someone below mentioned that magicians often exploit this for their tricks. I'm guessing people think of 7 first, since people are used to choosing between one and ten. Then, on reflection, they choose 17 instead since they want to have used the whole range of options.