A. Golbabai M. Javidi Application of He's homotopy perturbation method for nth-order integro-differential equations. 1409-1416 2007 190 Applied Mathematics and Computation 2 http://dx.doi.org/10.1016/j.amc.2007.02.018 db/journals/amc/amc190.html#GolbabaiJ07a