Both a number N and its half,when augmented by 1 (i.e.N+1 and N/2+1) form a perfect square.
0 is a trivial example.

List 4 more examples.

(In reply to re(2): Similar approach by broll)

It would seem that since I installed Skype on the machine from which I am working, even though I don't have Skype activated, Skype seems to check certain strings of numbers and displays them as a telephone number.  In the case of "3 1680 41 29",  the "3" (or 03 ) could represent the State code of Vic, Australia.

Checking some other sites it is similarly treating Australian phone numbers.  It's a bit disturbing seeing something like that where it's not meant to be.  May just have to report this oddity to Skype.
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Intriguing, with the quotes that mentioned behaviour is overriden.
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A search of the Skype site indicates that the feature can be turned off, TG!

Edited on December 25, 2010, 7:48 pm

Edited on December 25, 2010, 8:13 pm

Posted by brianjn on 2010-12-25 19:46:32