Dear Dirichlet, Issue 02

Dear Dirichlet

Moonlighting agony uncle Professor Dirichlet answers your personal problems. Want the Prof’s help? Send your problems to

Dear Dirichlet,

My wife and I are having difficulty with her shift times as a Northern line tube driver. We’re always tired when we see each other and I just feel that every point in our relationship ends up leading to an argument. Can you help?

— Complexified, High Barnet

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Page 3 model: The Duckworth–Lewis method

If there are two things that typify an English summer, they are cricket and rainy days. Unfortunately, the two very often come together, which makes it very difficult to decide who should win a limited overs cricket match when rain stops play.

In these cases, a statistical model known as the Duckworth–Lewis method, devised by statistician Frank Duckworth and mathematician Tony Lewis, settles the issue (and provokes copious debate amongst Lord’s Long
Room members as they sip their champagne).

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£100 Prize Crossnumber, Issue 02

Our original £100 prize crossnumber is featured on pages 44 and 45 of Issue 02.

Correction: There is an error in clue 4D. The 13th digit is actually larger than the 14th.
Clarification: In 40A ‘divisible’ should read ‘properly divisible’. The answer is not 2.
Clarification: In 9A ‘proper factors’ should be taken to mean factors not equal to the number. 1 should be included.


  • Although many of the clues have multiple answers, there is only one solution to the completed crossnumber. As usual, no numbers begin with 0. Use of Python, OEIS, Wikipedia, etc. is advised for some of the clues.
  • One randomly selected correct answer will win £100. Three randomly selected runners up will win a Chalkdust t-shirt. The prizes have been provided by G-Research, researchers of financial markets and investment ideas. Find out more at
  • To enter, submit the sum of the across clues via this form by 5 December 2015. Only one entry per person will be accepted. This competition has now ended. Winners will be notified by email and announced on our blog by 19 December 2015.

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