login
A279273
Number of 2 X 2 matrices having entries in {0,1,...,n} and determinant in the open interval (-n,n) with no entry repeated.
1
0, 0, 0, 8, 40, 104, 216, 440, 720, 1160, 1656, 2432, 3216, 4472, 5680, 7280, 9128, 11328, 13504, 16632, 19424, 23216, 27088, 31600, 35832, 41912, 47192, 53544, 60152, 68192, 75168
OFFSET
0,4
COMMENTS
a(n) mod 8 = 0.
LINKS
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) in range(-n+1, n):
s+=1
return s
for i in range(0, 122):
print str(i)+" "+str(t(i))
CROSSREFS
Cf. A211032 (where the entries can be repeated).
Sequence in context: A069083 A014642 A211631 * A143943 A135796 A105374
KEYWORD
nonn
AUTHOR
Indranil Ghosh, Dec 09 2016
STATUS
approved