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A293047
Number of odd permutations on {1,2,...,n} with exactly 2 weak excedances.
1
0, 0, 0, 3, 4, 15, 26, 63, 120, 255, 502, 1023, 2036, 4095, 8178, 16383, 32752, 65535, 131054, 262143, 524268, 1048575, 2097130, 4194303, 8388584, 16777215, 33554406, 67108863, 134217700, 268435455, 536870882, 1073741823, 2147483616, 4294967295, 8589934558
OFFSET
0,4
LINKS
Dmitry Efimov, Determinants of generalized binary band matrices, arXiv:1702.05655 [math.RA], 2017.
FORMULA
a(n) = (A000295(n) + (-1)^n * (n-1))/2, n > 0.
a(n) = 2^(n-1) - 1 for odd n.
CROSSREFS
Sequence in context: A081405 A167367 A024858 * A135100 A205485 A344261
KEYWORD
nonn
AUTHOR
Eric M. Schmidt, Oct 09 2017
STATUS
approved