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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.

A084611 a(n) = sum of absolute values of coefficients of (1+x-x^2)^n.

Table of values

n a(n)
0 1
1 3
2 7
3 13
4 35
5 83
6 165
7 367
8 899
9 1957
10 3839
11 9771
12 22709
13 43213
14 102963
15 255061
16 525601
17 1098339
18 2798273
19 6202969
20 11746259
21 29976073
22 70898649
23 140495779
24 314391789
25 787757461
26 1688887719
27 3337986541
28 8583687613
29 19647782463

List of values

[1, 3, 7, 13, 35, 83, 165, 367, 899, 1957, 3839, 9771, 22709, 43213, 102963, 255061, 525601, 1098339, 2798273, 6202969, 11746259, 29976073, 70898649, 140495779, 314391789, 787757461, 1688887719, 3337986541, 8583687613, 19647782463]

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

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