Hi. You probably still need to be a little clearer as to what you want.
What is the relationship between A and B?
If A can ONLY be chosen out of a selection of 16 possible options, and each of those options can have only ONE corresponding value in B, then a lookup table would be appropriate. In that instance I would expect that somewhere within your spreadsheet you have a table outlining those 16 options and their corresponding values.
Assuming this is correct, and that your Table is in C1 to D17, and again assuming the value that A2 is the first value you want to check;
B2 will contain the formula =VLOOKUP(A2,$C$1:$D$17,2,FALSE)
B3 will contain the formula =VLOOKUP(A3,$C$1:$D$17,2,FALSE)
B4 will contain the formula =VLOOKUP(A4,$C$1:$D$17,2,FALSE)