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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
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
KEYWORD
nonn
AUTHOR
Indranil Ghosh, Nov 30 2016
STATUS
approved