A201686 a(n) = binomial(n, [n/2]) - 2.

-1, -1, 0, 1, 4, 8, 18, 33, 68, 124, 250, 460, 922, 1714, 3430, 6433, 12868, 24308, 48618, 92376, 184754, 352714, 705430, 1352076, 2704154, 5200298, 10400598, 20058298, 40116598, 77558758, 155117518, 300540193, 601080388, 1166803108, 2333606218, 4537567648, 9075135298, 17672631898, 35345263798, 68923264408, 137846528818

Offset

0,5

Links

Table of n, a(n) for n=0..40.

J.-L. Baril, Classical sequences revisited with permutations avoiding dotted pattern, Electronic Journal of Combinatorics, 18 (2011), #P178. See Table 3.

Formula

Conjecture: +(n+1)*a(n) +2*(-n-1)*a(n-1) +(-3*n+7)*a(n-2) +2*(4*n-9)*a(n-3) +4*(-n+3)*a(n-4)=0. - R. J. Mathar, Jul 17 2014

Mathematica

Table[Binomial[n, Floor[n/2]]-2, {n, 0, 40}] (* Harvey P. Dale, Apr 12 2018 *)

Crossrefs

Cf. A001405.

Sequence in context: A001977 A008373 A008374 * A008240 A008375 A056309

Adjacent sequences: A201683 A201684 A201685 * A201687 A201688 A201689

Keyword

sign

Author

N. J. A. Sloane, Dec 03 2011

Status

approved