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

0,7

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..285 from Indranil Ghosh)

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)==a+d:
                            s+=1
    return s
for i in range(0, 286):
    print str(i)+" "+str(t(i))

Crossrefs

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

Sequence in context: A071339 A146890 A168273 * A351838 A377783 A328527

Adjacent sequences: A278930 A278931 A278932 * A278934 A278935 A278936

Keyword

nonn

Author

Indranil Ghosh, Dec 02 2016

Status

approved