perplexus.info :: Sequences : Divisible

Divisible (Posted on 2011-09-30)

Five single-digit positive integers appear in a sequence.

The sum of the first two is divisible by the second, but not by the first.
The sum of the first three is divisible by the third, but not by the first or the second.
The sum of the first four is divisible by the fourth, but not by the first, second or third.
The sum of the first five is divisible by the fifth, but not by the first, second, third or fourth.

What are the five integers, in order?

See The Solution Submitted by Charlie

Rating: 4.0000 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)

Second effort (spoiler)

| Comment 3 of 6 |

Well yes, I did miss an option. Let's do it correctly:

Note:

1) The 5 digits must be different

2) The 1st, 2nd, 3rd and 4th digits cannot be 1, because 1 divides the sum of the 5 digits.

3) The first digit must be a multiple of the 2nd digit

The only possibility for the first two digits are therefore

4) The third digit must divide the sum of the first two, but it cannot be a multiple of the 2nd digit.

4 + 2 = 6, which makes 423 a possibility for the 1st 3 digits

6 + 2 = 8, so nothing works as a 3rd digit

8 + 2 = 10, which makes 825 a possibility

9 + 3 = 12, which makes both 932 and 934 possibilities

8 + 4 = 12, which makes 843 and 846 a possibility

recapping, the first 3 digits must be

423

825

932

934

843 or

846

5) The 4th digit must divide the sum of the first three. but it cannot be a multiple of any of the first 3

4+2+3 = 9, so nothing works as a 4th digit

8+2+5 = 15, but 3 cannot be the 4th digit, because 2 divides 18

9+3+2 = 14, but 7 cannot be the 4th digit, because 3 divides 21

9+3+4 = 16, but 2 does not work because 3 divides 18

8+4+3 = 15, but 4 does not work because 4 divides 20

8+4+6 = 18, and 9 does not work but 3 does

recapping, the first 4 digits can only be 8463

6) The 5th digit must divide the sum of the first 4

8+4+6+3 = 21, and 7 does not work (because 4 divides 28), so the first 5 digits can only be 84631

And this time I'll check

8+4 = 12 is divisible by 4 but not 8

8+4+6 = 18 is divisible by 6, but not 4 or 8

8+4+6+3 = 21 is divisible by 3, but not 4,6,8

8+4+6+3+1 = 22 is divisible by 1, but not 3,4,6,8

Nice puzzle, charlie!

Posted by Steve Herman on 2011-10-01 01:10:41

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