The i-th uniform B-spline basis function of a given degree
BSplineBasis[d, x]
BSplineBasis[d, n, x]
BSplineBasis[{d, {u1, u2, …}}, n, x]
BSplineBasis[3, 0.5]
→ 0.6666666666666666Plot[BSplineBasis[3, x], {x, 0, 1}]
→ -Graphics-D[BSplineBasis[{2, knots}, 2, x], {x, 1}]
→ Derivative[{0, 0}, 0, 1][BSplineBasis][{2, knots}, 2, x]