A282084 Number of n-element subsets of [n+8] having an even sum.

1, 4, 20, 85, 255, 636, 1484, 3235, 6470, 12120, 21816, 37854, 63090, 101640, 159720, 245322, 367983, 540540, 780780, 1110395, 1554553, 2145572, 2925780, 3945045, 5260060, 6941168, 9076912, 11769100, 15131700, 19302480, 24449808, 30763812, 38454765, 47771700

Offset

0,2

Links

Alois P. Heinz, Table of n, a(n) for n = 0..1000

Formula

G.f.: -(x^2-x+1)*(x^8-4*x^7+20*x^6-36*x^5+54*x^4-36*x^3+20*x^2-4*x+1) / ((x^2+1)^5*(x-1)^9).

a(n) = A282011(n+8,n).

Example

a(0) = 1: {}.
a(1) = 4: {2}, {4}, {6}, {8}.
a(2) = 20: {1,3}, {1,5}, {1,7}, {1,9}, {2,4}, {2,6}, {2,8}, {2,10}, {3,5}, {3,7}, {3,9}, {4,6}, {4,8}, {4,10}, {5,7}, {5,9}, {6,8}, {6,10}, {7,9}, {8,10}.

Crossrefs

Cf. A282011.

Sequence in context: A246936 A110154 A158608 * A262768 A250003 A343361

Adjacent sequences: A282081 A282082 A282083 * A282085 A282086 A282087

Keyword

nonn,easy

Author

Alois P. Heinz, Feb 05 2017

Status

approved