asp.net validation

I'm using the code below to format a txtbox on my web page. The code works fine, it accepts input like this: 1C232. I need to change the code so the second character could be either a number or letter...thanks.

VB Code:

ValidationExpression="\d{1}[a-z]\d{3}

have you tried

Code:

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\d{1}[0-9][a-z]\d{3}

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this worked to format.

VB Code:

ValidationExpression="\d{1}[a-zA-Z0-9]\d{3}