LDA #1        3   1
STA A         430
LDA #2        3   2
STA B         431
LOOP: OUT A   230
LDA A         330
ADD B         531
STA A         430
INC B        1231
JMP LOOP      706

Of course A & B didn't have to use boxes 30 & 31 ... in fact once we'd worked out that the last box we needed for the program was 11, we could have used any boxes from 12 onwards.