

A160255


The sum of all the entries in an n X n Cayley table for multiplication in Z_n.


2



0, 1, 6, 16, 40, 63, 126, 176, 270, 365, 550, 624, 936, 1099, 1350, 1664, 2176, 2349, 3078, 3280, 3948, 4631, 5566, 5712, 7000, 7813, 8748, 9520, 11368, 11475, 13950, 14592, 16236, 17969, 19390, 20304, 23976, 25327, 27222, 28400, 32800, 32949, 37926, 38896
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OFFSET

1,3


COMMENTS

Thanks to David Miller.


LINKS

Table of n, a(n) for n=1..44.


FORMULA

a(p) = (p1)*(p^2p)/2, for p prime.
a(n) = (n/2)*Sum_{i=1..n1} gcd(n,i)*(n/gcd(n,i)1). [Edited by Richard L. Ollerton, May 06 2021]
a(n) = (n^2/2)*Sum_{dn} phi(d)*(d1)/d, where phi = A000010.  Richard L. Ollerton, May 06 2021
From Ridouane Oudra, Aug 24 2022: (Start)
a(n) = Sum_{i=1..n} Sum_{j=1..n} (i*j mod n);
a(n) = n^3/2  (n/2)*Sum_{i=1..n} gcd(n,i);
a(n) = n^3/2  (n/2)*Sum_{dn} d*tau(d)*moebius(n/d);
a(n) = (A000578(n)  n*A018804(n))/2. (End)


EXAMPLE

For n=4:
 0 1 2 3
+
0 0 0 0 0
1 0 1 2 3
2 0 2 0 2
3 0 3 2 1
Sum becomes 6+4+6 = 16.


PROG

(PARI) a(n) = (n/2)*sum(i=1, n1, gcd(n, i)*(n/gcd(n, i)1)); \\ Michel Marcus, Jun 16 2013 [edited by Richard L. Ollerton, May 06 2021]


CROSSREFS

Cf. A000010, A000578, A018804.
Sequence in context: A130902 A300371 A009955 * A213667 A123205 A123607
Adjacent sequences: A160252 A160253 A160254 * A160256 A160257 A160258


KEYWORD

nonn


AUTHOR

David Byrne (david.roggeveen.byrne(AT)gmail.com), May 06 2009


EXTENSIONS

More terms from Carl Najafi, Sep 29 2011


STATUS

approved



