cp's OEIS Frontend

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.

A071721 Expansion of (1+x^2*C^2)*C^2, where C = (1-(1-4*x)^(1/2))/(2*x) is g.f. for Catalan numbers, A000108.

Table of values

n a(n)
0 1
1 2
2 6
3 18
4 56
5 180
6 594
7 2002
8 6864
9 23868
10 83980
11 298452
12 1069776
13 3863080
14 14040810
15 51325650
16 188574240
17 695987820
18 2579248980
19 9593714460
20 35804293200
21 134032593240
22 503154100020
23 1893689067348
24 7144084508256

List of values

[1, 2, 6, 18, 56, 180, 594, 2002, 6864, 23868, 83980, 298452, 1069776, 3863080, 14040810, 51325650, 188574240, 695987820, 2579248980, 9593714460, 35804293200, 134032593240, 503154100020, 1893689067348, 7144084508256]