a4 = 3*4 = 12. Answer: 3,6,9,12. 3) an = 3n – 5 a1 = 3*1-5 = -2 a2 = 3*2 – 5 = 1 a3 = 3*3-5 = 4 a4 = 3*4 – 5 = 7 Answer: -2,1,4,7. 5) an = 3n a1 = 31= 3 ... 21) an = (-1)n; a50. Answer: a50 = (-1)50 = 1. 23) an = ;a12. Answer: #25-40: write an expression for the nth term of the sequence. 25) 2,4,6,8,10…. Answer: an = 2n ...