Write a recursive formula for the following sequence: 3, 6, 12, 24, ....

an = an – 1 + 3; A1 = 3
an = an – 1 + 3n; A1 = 3
an = 2an – 1; A1 = 3
an = 3an – 1 – 3; A1 = 3
none of these