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id	challengeType	title	forumTopicId
5900f49d1000cf542c50ffb0	5	Problem 305: Reflexive Position	301959

Description

Let's call S the (infinite) string that is made by concatenating the consecutive positive integers (starting from 1) written down in base 10. Thus, S = 1234567891011121314151617181920212223242...

It's easy to see that any number will show up an infinite number of times in S.

Let's call f(n) the starting position of the nth occurrence of n in S. For example, f(1)=1, f(5)=81, f(12)=271 and f(7780)=111111365.

Find ∑f(3k) for 1≤k≤13.

Instructions

Tests

tests:
  - text: <code>euler305()</code> should return 18174995535140.
    testString: assert.strictEqual(euler305(), 18174995535140);

Challenge Seed

function euler305() {
  // Good luck!
  return true;
}

euler305();

Solution

// solution required

1.1 KiB Raw Blame History