Proper formula for p value

Does anyone have idia about how to calculate exact p value for the distributions like t,f,chi-square,normal,binomial and poisson.? I know that it come directly from the statistical softwares like sas,spss but i want proper formula to evaluate p value. for example if paired t test = 2.12 for 98 df then any statistical software reply p value=0.0363......it is not statistically significant because it is <0.05. but i want formula for p value not procedure on software. If any statistician know it then please reply. also reply on atulvw@rediffmail.com