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 A279018 Number of 2 X 2 matrices having entries in {-n,...,0,..,n} and permanent=trace with no entry repeated. 2
 0, 0, 8, 24, 56, 100, 156, 236, 320, 408, 540, 692, 844, 1044, 1228, 1368, 1592, 1884, 2180, 2500, 2764, 2996, 3356, 3756, 4080, 4456, 4884, 5276, 5740, 6252, 6740, 7316, 7868, 8340, 8860, 9352, 9896, 10628, 11324 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Indranil Ghosh, Table of n, a(n) for n = 0..150 MATHEMATICA f[n_] := f[n] = Block[{a, b, c, d, s = 0}, a = -n; While[a < n +1, b = -n; While[b < n +1, c = -n; While[c < n +1, d = -n; While[d < n +1, If[ a != b && a != c && a != d && b != c && b != d && c != d && a*d + b*c == a + d, s++]; d++]; c++]; b++]; a++]; s]; Array[f, 40, 0] (* Robert G. Wilson v, Dec 03 2016 *) 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!=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, 151): print str(i)+" "+str(t(i)) CROSSREFS Cf. A211145 (wherein the entries can be repeated). Sequence in context: A212972 A316541 A152134 * A011925 A256052 A159741 Adjacent sequences: A279015 A279016 A279017 * A279019 A279020 A279021 KEYWORD nonn AUTHOR Indranil Ghosh, Dec 03 2016 STATUS approved

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Last modified June 20 16:01 EDT 2024. Contains 373526 sequences. (Running on oeis4.)