piano chord
D11
D1F♯3A5C♭7E9G11
Six notes in theory; in practice the third is usually dropped, because the eleventh sits a half step above it.
What is true of it
D11 is D, F♯, A, C, E and G — 1, 3, 5, b7, 9 and 11 counted from D.
On an instrument that cannot reach all 6, the 3, 5 and 1 go first, in that order.