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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.

A084780 a(n) = sum of absolute-valued coefficients of (1+3*x-x^2)^n.

Table of values

n a(n)
0 1
1 5
2 21
3 77
4 291
5 1119
6 3523
7 15007
8 50923
9 182669
10 701121
11 2379129
12 8909361
13 32490021
14 106309861
15 423990203
16 1456199483
17 5089398187
18 19942506259
19 65753622619
20 252337832801
21 903751067081
22 3026099773993
23 11771846189609

List of values

[1, 5, 21, 77, 291, 1119, 3523, 15007, 50923, 182669, 701121, 2379129, 8909361, 32490021, 106309861, 423990203, 1456199483, 5089398187, 19942506259, 65753622619, 252337832801, 903751067081, 3026099773993, 11771846189609]

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

Content is available under The OEIS End-User License Agreement.