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%I #16 Dec 10 2016 22:37:47
%S 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,
%T 72,76,84,84,96,96,104,108,112,116,128,128,132,136,148,148,160,160,
%U 168,176,180,180,196,196,204
%N Number of 2 X 2 matrices with entries in {0,1,...,n} and permanent = trace with no entry repeated.
%C a(n) mod 4 = 0.
%H Indranil Ghosh and Chai Wah Wu, <a href="/A278933/b278933.txt">Table of n, a(n) for n = 0..10000</a> (terms for n = 0..285 from Indranil Ghosh)
%o (Python)
%o def t(n):
%o s=0
%o for a in range(0,n+1):
%o for b in range(0,n+1):
%o for c in range(0,n+1):
%o for d in range(0,n+1):
%o if (a!=b and a!=d and b!=d and c!=a and c!=b and c!=d):
%o if (a*d+b*c)==a+d:
%o s+=1
%o return s
%o for i in range(0,286):
%o print str(i)+" "+str(t(i))
%Y Cf. A210288 (wherein the entries can be repeated).
%K nonn
%O 0,7
%A _Indranil Ghosh_, Dec 02 2016