A278902 - OEIS

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A278902

Number of 2 X 2 matrices with entries in {0,1,...,n} with determinant = trace and no entry repeated.

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(n+1):

for b in range(n+1):

for c in range(n+1):

for d in range(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(241):

print(str(i)+" "+str(t(i)))

CROSSREFS

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

Sequence in context: A368549 A326994 A367146 * A336583 A333754 A088525

Adjacent sequences: A278899 A278900 A278901 * A278903 A278904 A278905

KEYWORD

nonn

AUTHOR

Indranil Ghosh, Nov 30 2016

STATUS

approved