1 |
1×4 |
1 |
4×7 |
1 |
(3n-2)×(3n+1) |
1 |
1×4 |
1 |
4×7 |
1 |
(3n-2)×(3n+1) |
3 |
1×4 |
3 |
4×7 |
3 |
(3n-2)×(3n+1) |
1 |
4 |
1 |
4 |
1 |
7 |
1 |
(3n-2) |
1 |
(3n+1) |
1 |
(3n+1) |
3n |
(3n+1) |
n |
(3n+1) |
n |
(3n+1) |
A.1340 | B.1338 | C.670 | D.669 |
1 |
1+2 |
1 |
1+2+3 |
1 |
1+2+3+…+n |
A.1022 | B.1024 | C.1026 | D.1028 |
1 |
anan+1 |
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