In mathematics, Nielsen's spiral, also called the sici spiral is the spiral with parametric equations
- <math>x = a\,\mbox{ci}\,t \,</math>
- <math>y = a\,\mbox{si}\,t \,</math>
where "ci" is the cosine integral and "si" is the sine integral. This curve is notable because its curvature increases at a constant rate along its length.
