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

Download Crossnumber #2 as a PDF, or read on!

Submit your answer This competition has now ended.

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.

Rules

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 gresearch.co.uk.

. 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 gresearch.co.uk. 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.

Crossnumber

Crossnumber #2, set by Humbug:

Clues

Across

1. A multiple of 24A. (6)

5. It is possible to construct a regular polygon with this number of sides using only a ruler and compass. (5)

7. The number of factors of this number is equal to its fourth root. (7)

9. A number with 9 proper factors. (2)

11. The first four digits of 4D. (4)

12. A prime number. (3)

13. 30D multiplied by 12A. (6)

16. The least number of pence which cannot be made using less than 5 coins. (2)

17. Two less than a triangular number. (4)

19. The number of consecutive non-prime numbers starting at (and including) 370262. (3)

21. A prime number. (3)

22. The smallest number with a (multiplicative) persistence of 11. (15)

24. The lowest number k such that when $3^k$ is divided by k the remainder is 24. (3)

25. When written as a Roman numeral, this number is an anagram of LCD. (3)

26. A year which began or will begin on a Wednesday. (4)

28. A multiple of 9. (2)

29. All the digits of this number are the same. (6)

31. A square number. (3)

33. The last four digits of 4D. (4)

35. The minimum number of knights needed so that each square on a chessboard is either occupied or attacked by a knight. (2)

36. The number of primes less than 100,000,000. (7)

39. This number is both square and tetrahedral. (5)

40. The smallest even number, n, such that $2^n-2$ is properly divisible by n. (6)

Down