Question 779764
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 1st term =  3<sup>1</sup>+1 = 3+1 = 4
 2nd term =  3<sup>2</sup>-1 = 9-1 = 8
 3rd term =  3<sup>3</sup>+1 = 27+1 = 28
 4th term =  3<sup>4</sup>-1 = 81-1 = 80
 5th term =  3<sup>5</sup>+1 = 243+1 = 244
 6th term =  3<sup>6</sup>-1 = 729-1 = 728
 7th term =  3<sup>7</sup>+1 = 2187+1 = 2188
 8th term =  3<sup>8</sup>-1 = 6561-1 = 6560
 9th term =  3<sup>9</sup>+1 = 19683+1 = 19684
10th term = 3<sup>10</sup>-1 = 59049-1 = 59048
11th term = 3<sup>11</sup>+1 = 177147+1 = 177148
12th term = 3<sup>12</sup>-1 = 531441-1 = 531440
13th term = 3<sup>13</sup>+1 = 1594323+1 = 1594324
14th term = 3<sup>14</sup>-1 = 4782969-1 = 4782968
15th term = 3<sup>15</sup>+1 = 14348907+1 = 14348908
16th term = 3<sup>16</sup>-1 = 43046721-1 = 43046720
17th term = 3<sup>17</sup>+1 = 129140163+1 = 129140164
18th term = 3<sup>18</sup>-1 = 387420489-1 = 387420488
19th term = 3<sup>19</sup>+1 = 1162261467+1 = 1162261468
20th term = 3<sup>20</sup>-1 = 3486784401-1 = 3486784400
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Edwin</pre>