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A278902 Number of 2 X 2 matrices with entries in {0,1,...,n} with determinant = trace and no entry repeated. 2
0, 0, 0, 0, 0, 8, 12, 24, 28, 40, 48, 68, 72, 100, 120, 132, 144, 188, 208, 252, 280, 304, 336, 396, 416, 464, 512, 556, 592, 668, 704, 776, 844, 900, 960, 1020, 1056, 1148, 1240, 1308, 1348, 1456, 1524, 1628, 1728, 1792, 1872, 2004, 2080, 2188, 2292 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

a(n) mod 4=0.

LINKS

Indranil Ghosh and Chai Wah Wu, Table of n, a(n) for n = 0..10000 (terms for n = 0..240 from Indranil Ghosh)

PROG

(Python)

def t(n):

    s=0

    for a in range(0, n+1):

        for b in range(0, n+1):

            for c in range(0, n+1):

                for d in range(0, n+1):

                    if (a!=b  and a!=d and b!=d and c!=a and c!=b and c!=d):

                        if (a*d-b*c)==a+d:

                            s+=1

    return s

for i in range(0, 241):

    print str(i)+" "+str(t(i))

CROSSREFS

Cf. A210286 (wherein the entries can be repeated).

Sequence in context: A105571 A141616 A326994 * A088525 A054735 A162691

Adjacent sequences:  A278899 A278900 A278901 * A278903 A278904 A278905

KEYWORD

nonn

AUTHOR

Indranil Ghosh, Nov 30 2016

STATUS

approved

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Last modified December 10 04:15 EST 2019. Contains 329885 sequences. (Running on oeis4.)