To accomplish this, you'll need to use an open end question or a free format question instead of a numeric question. Either way, you can use custom JavaScript verification to ensure that the answer is a number. Here's an example verification that requires the response to be only numerical characters:
if (!/^[0-9]+$/.test(SSI_GetValue('OpenEndQ'))) {
strErrorMessage = 'Not a number.';
}
If you tell me any specific requirements you want for this number (e.g., negative numbers, minimum or maximum values, decimals), I can adjust the code for you.