All the required math is online, of course. The issue is that different people have different gaps in their math education and many are unable to tell where those gaps start and how to fill them. A useful post/sequence/app would construct the pyramid of the math knowledge and skills required for not being stumped by whatever math is in the sequences, let people test their mastery of each piece, map out the gaps and direct them to the relevant online resources in the suitable order. Not sure how much interest is there among the LWers who are qualified to do such a job.