SOLUTION: What will be the next number of the following series: 1,1,2,4,6,18,21,? a)84 b)63 c)78 d)28

Question 884472: What will be the next number of the following series: 1,1,2,4,6,18,21,?
a)84 b)63 c)78 d)28
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
Any of them could be.
That is the nature of sequences.
a)84
1 0 1 0 -1 12 -52 209
1 1 1 -1 11 -40 157 209
2 2 0 10 -29 117 366
4 2 10 -19 88 483
6 12 -9 69 571
18 3 60 640
21 63 700
84 763
847
9th term 847
b 63
1 0 1 0 -1 12 -52 188
1 1 1 -1 11 -40 136 188
2 2 0 10 -29 96 324
4 2 10 -19 67 420
6 12 -9 48 487
18 3 39 535
21 42 574
63 616
679
9th term 679
c 78
1 0 1 0 -1 12 -52 203
1 1 1 -1 11 -40 151 203
2 2 0 10 -29 111 354
4 2 10 -19 82 465
6 12 -9 63 547
18 3 54 610
21 57 664
78 721
799
9th term 799
d) 28
1 0 1 0 -1 12 -52 153
1 1 1 -1 11 -40 101 153
2 2 0 10 -29 61 254
4 2 10 -19 32 315
6 12 -9 13 347
18 3 4 360
21 7 364
28 371
399
9th term 399
84
Multiply by 1, add 1, multiply by 2, add 2, etc.
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