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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.

A268618 a(n) = (2/n^3) * Sum_{d|n} moebius(n/d)*binomial(3*d,d).

Table of values

n a(n)
1 6
2 3
3 6
4 15
5 48
6 171
7 678
8 2871
9 12858
10 60084
11 290814
12 1448679
13 7394106
14 38527779
15 204365880
16 1101000087
17 6013054788
18 33239486925
19 185736687366
20 1047961118940
21 5964676687668
22 34219227608607
23 197737647050742
24 1150211467134927
25 6731334034067058
26 39614408616493581
27 234342269725331130
28 1392933275876114127

List of values

[6, 3, 6, 15, 48, 171, 678, 2871, 12858, 60084, 290814, 1448679, 7394106, 38527779, 204365880, 1101000087, 6013054788, 33239486925, 185736687366, 1047961118940, 5964676687668, 34219227608607, 197737647050742, 1150211467134927, 6731334034067058, 39614408616493581, 234342269725331130, 1392933275876114127]

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

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