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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.

A081875 a(n) = Sum_{d|n} phi(n/d)*C(2*d,d)/2.

Table of values

n a(n)
1 1
2 4
3 12
4 40
5 130
6 480
7 1722
8 6480
9 24336
10 92520
11 352726
12 1352640
13 5200312
14 20060040
15 77559060
16 300546720
17 1166803126
18 4537592928
19 17672631918
20 68923357200
21 269128940724
22 1052049834616
23 4116715363822
24 16123803207552

List of values

[1, 4, 12, 40, 130, 480, 1722, 6480, 24336, 92520, 352726, 1352640, 5200312, 20060040, 77559060, 300546720, 1166803126, 4537592928, 17672631918, 68923357200, 269128940724, 1052049834616, 4116715363822, 16123803207552]

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

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