Parent 1 and 2 have each 5 possible genotypes (OO, AO, BB, BO and AB).
Here a Punnett square with each possibilities. I highlighted the possible parent genotypes.
The total number of possible crosses is exactly 21. Note that here A = Ia, B = Ib and O = i.
This is starting from the information based on your blood type only (i.e. no information about your genotype).
Some background information. Antigen expressing alleles (here referred as Ia or A and Ib or B) are dominant. Not expressing an allele is notated i or O. Being of blood type O is when you don't express both alleles so it is a recessive trait (only possible genotype is ii or OO genotype).