InfoPath Dev

Infopath 2010 I Would like to check the last digit in a social security number if it's 1, 3, 5, 7, 9 then set option button value 1 else set option button value 2 how can this be done ?

Try setting the default value formula for the option button field to this:

2 - (substring(SocialSecurity, string-length(SocialSecurity), 1) mod 2)