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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.

A357421 a(n) is the hafnian of the 2n X 2n symmetric matrix whose generic element M[i,j] is equal to the digital root of i*j.

Table of values

n a(n)
0 1
1 2
2 54
3 1377
4 55350
5 4164534
6 217595322
7 11974135554
8 999599777190
9 150051627647010
10 11873389098337236

List of values

[1, 2, 54, 1377, 55350, 4164534, 217595322, 11974135554, 999599777190, 150051627647010, 11873389098337236]

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

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