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A278933 Number of 2 X 2 matrices with entries in {0,1,...,n} and permanent = trace with no entry repeated. 2
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 (list; graph; refs; listen; history; text; internal format)
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 * A145447 A204989 A101921

Adjacent sequences:  A278930 A278931 A278932 * A278934 A278935 A278936

KEYWORD

nonn

AUTHOR

Indranil Ghosh, Dec 02 2016

STATUS

approved

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Last modified October 17 16:18 EDT 2018. Contains 316285 sequences. (Running on oeis4.)