A293046 Number of even permutations on {1,2,...,n} with exactly 2 weak excedances.

0, 0, 1, 1, 7, 11, 31, 57, 127, 247, 511, 1013, 2047, 4083, 8191, 16369, 32767, 65519, 131071, 262125, 524287, 1048555, 2097151, 4194281, 8388607, 16777191, 33554431, 67108837, 134217727, 268435427, 536870911, 1073741793, 2147483647, 4294967263, 8589934591

Offset

0,5

Links

Table of n, a(n) for n=0..34.

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 even n > 0.

Crossrefs

Cf. A000295, A293047.

Sequence in context: A046861 A078917 A291349 * A213176 A236143 A084443

Adjacent sequences: A293043 A293044 A293045 * A293047 A293048 A293049

Keyword

nonn

Author

Eric M. Schmidt, Oct 09 2017

Status

approved