30th
Convert the number to a series of 1s - so 4 becomes 1111 - and use this regex to check if it’s prime.
/^1?$|^(11+?)\1+$/
Very clever. Read this for an explanation.
According to this analysis of 100 million publicly-available profiles on Facebook, the most popular first names are John, David and Michael while the most popular last names are Smith, Jones and Johnson.

I just spotted this Google search print advertisement in the Ahmedabad edition (or Jaipur edition) of the Times of India.
In a recently conducted international programming contest, China topped with 20 finalists (out of 894 participants), followed by Russia with 10 finalists (out of 380 participants), and the US with 2 finalists (out of 234 participants).
India could not manage a single finalist from its 705 participants.
Google App Engine seems to have quietly moved the date of quota changes from the originally announced May 25th to June 22nd.
The quota values appear to be the same though.
The world’s most difficult word to translate has been identified as “ilunga” - “a person who is ready to forgive any abuse for the first time, to tolerate it a second time, but never a third time” - from the Tshiluba language spoken in south-eastern DR Congo.
Google’s transliteration service is available in four additional languages: Bengali, Gujarati, Marathi and Nepali.