The Kurt Mahler Archive

Thanks to the hard work of Jon Borwein, Yann Bugeaud, Michael Coons, and the late Alf van der Poorten, there is now an online archive of the works of the number theorist Kurt Mahler. This is a great resource for mathematicians and more initiatives like this are needed.

I'll just mention one open problem from Kurt Mahler's last paper: what are the positive integers n, not divisible by 7, such that n² has only digits 0 and 1 when expressed in base 7? The only examples known are n = 1 and n = 20. There are no other solutions with n < 1.67 · 10¹¹.