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A131231 as a triangular array

1
61
731
12131
133131
1813131
19313131
241313131
2531313131

A131231 as a square array

167121318192425
13131313
1313131
131313
13131
1313
131
13
1
167121318192425
13131313
1313131
131313
13131
1313
131
13
1