OFFSET
0,2
LINKS
Indranil Ghosh, Table of n, a(n) for n = 0..155
EXAMPLE
For n = 2, few of the possible matrices are [-2,-2,0,0], [-2,-1,0,0], [-2,0,-2,0], [-2,0,-1,0], [-2,0,0,0], [-2,0,1,0], [-2,0,2,0], [1,0,0,0], [1,0,1,0], [1,0,2,0], [1,1,0,0], [1,2,0,0], [2,-2,0,0], [2,-1,0,0], [2,0,-2,0], .... There are 81 possibilities. Here each of the matrices is defined as M = [a,b,c,d] where a = M[1][1], b = M[1][2], c = M[2][1], d = M[2][2]. So for n = 2, a(n)=81.
PROG
(Python)
def t(n):
s=0
for a in range(-n, n+1):
for b in range(-n, n+1):
for c in range(-n, n+1):
for d in range(-n, n+1):
if (a*d-b*c)*n==(a*d+b*c):
s+=1
return s
for i in range(0, 156):
print str(i)+" "+str(t(i))
CROSSREFS
KEYWORD
nonn
AUTHOR
Indranil Ghosh, Jan 06 2017
STATUS
approved