Arithmetic or common difference like 4,7,10,13,16,...
their common difference is 3.4 is the 1st nth term or a1,7 is the 2nd term or a2. if you want to get the a15 you just follow this formula an=a1+(n-1)d
a15=4+(15-1)3 a15=4+(14)3 a15=4+42 a15=46.
d= common difference