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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.

A268617 a(n) = (1/n^2) * Sum_{d|n} moebius(n/d)*binomial(3*d,d).

Table of values

n a(n)
1 3
2 3
3 9
4 30
5 120
6 513
7 2373
8 11484
9 57861
10 300420
11 1599477
12 8692074
13 48061689
14 269694453
15 1532744100
16 8808000696
17 51110965698
18 299155382325
19 1764498529977
20 10479611189400
21 62629105220514
22 376411503694677
23 2273982941083533
24 13802537605619124
25 84141675425838225
26 514987312014416553
27 3163620641291970255

List of values

[3, 3, 9, 30, 120, 513, 2373, 11484, 57861, 300420, 1599477, 8692074, 48061689, 269694453, 1532744100, 8808000696, 51110965698, 299155382325, 1764498529977, 10479611189400, 62629105220514, 376411503694677, 2273982941083533, 13802537605619124, 84141675425838225, 514987312014416553, 3163620641291970255]

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

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