A278933 Number of 2 X 2 matrices with entries in {0,1,...,n} and permanent = trace with no entry repeated.

0, 0, 0, 0, 0, 0, 4, 4, 8, 8, 12, 12, 20, 20, 24, 28, 32, 32, 40, 40, 48, 52, 56, 56, 68, 68, 72, 76, 84, 84, 96, 96, 104, 108, 112, 116, 128, 128, 132, 136, 148, 148, 160, 160, 168, 176, 180, 180, 196, 196, 204

Offset: 0

Author

Indranil Ghosh, Dec 02 2016

Keywords

• nonn

Comments

a(n) mod 4 = 0.

Links

• Chai Wah Wu, Table of n, a(n) for n = 0..10000 (terms for n = 0..285 from Indranil Ghosh)

Crossrefs

Cf. A210288 (wherein the entries can be repeated).

Programs

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(0,286):
    print(t(i), end=', ')