Dear list members,
Firstly thank you for all the replies.

Dory Heilijgers wrote:

The book by Gonda is his Change and continuity in Indian religion, with an article ‘The number sixteen.’ As I remember well he also discusses other numbers.

Does anyone have a pdf of this.?

Also I was given this reference offlist which looks very promising. Does anyone have  a pdf of:
Lucky Numbers in Ancient Indian Literature by Siegfried Lienhard.
Its in:

 Veroffentlichungen der Glasenapp-Stiftung 44
Siegfried Lienhard: Kleine Schriften
Edited by Oskar von Hinuber, 2008

page 159-173

and in:

Langue, style et structure dans le monde Indian, Paris, 1996, 523-536


Thanks,
Harry Spier