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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A059219 Variation of Boustrophedon transform applied to sequence 1,0,0,0,...: fill an array by diagonals in alternating directions - 'up' and 'down'. The first element of each diagonal after the first is 0. When 'going up', add to the previous element the elements of the row the new element is in. When 'going down', add to the previous element the elements of the column the new element is in. The final element of the n-th diagonal is a(n).

Table of values

n a(n)
0 1
1 1
2 2
3 5
4 15
5 55
6 239
7 1199
8 6810
9 43108
10 300731
11 2291162
12 18923688
13 168402163
14 1606199354
15 16345042652
16 176758631046
17 2024225038882
18 24471719797265
19 311446235344127
20 4162172487402027
21 58275220793611957
22 853045299274146032

List of values

[1, 1, 2, 5, 15, 55, 239, 1199, 6810, 43108, 300731, 2291162, 18923688, 168402163, 1606199354, 16345042652, 176758631046, 2024225038882, 24471719797265, 311446235344127, 4162172487402027, 58275220793611957, 853045299274146032]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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