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%I #4 Oct 09 2017 23:21:57
%S 0,0,0,3,4,15,26,63,120,255,502,1023,2036,4095,8178,16383,32752,65535,
%T 131054,262143,524268,1048575,2097130,4194303,8388584,16777215,
%U 33554406,67108863,134217700,268435455,536870882,1073741823,2147483616,4294967295,8589934558
%N Number of odd permutations on {1,2,...,n} with exactly 2 weak excedances.
%H Dmitry Efimov, <a href="https://arxiv.org/abs/1702.05655">Determinants of generalized binary band matrices</a>, arXiv:1702.05655 [math.RA], 2017.
%F a(n) = (A000295(n) + (-1)^n * (n-1))/2, n > 0.
%F a(n) = 2^(n-1) - 1 for odd n.
%Y Cf. A000295, A293046.
%K nonn
%O 0,4
%A _Eric M. Schmidt_, Oct 09 2017