Dear Paolo,

Although it is not quite on tantra, there is a highly interesting article in modern Sanskrit on the relationship between Sanskrit analysis of poetic metre and Pascal's triangle. I do not have the full reference available in my present location, but it may be found in the introduction to the late Michael Hahn's edition of the ChandoratnAkara, which may be available on his academia page, if that is still accessible.

In Buddhist tantra, quite a lot has been written on the mathematics of the KAlacakratantra. The late Edward Henning's webpage kalacakra.org has some useful material on this, as does Henning's book, KAlacakra and the Tibetan Calendar.

There is also quite a lot on this in German, by Dieter Schuh, but exclusively concerned with the Tibetan legacy of the Indian sources and not with the Indian materials themselves.

best,

Matthew