You are dealing with a Cyclic Numbers in your given Example. Like you are mentioning 258,741 so, Here are some interesting properties of Cyclic Numbers:
2+5+8+7+4+1=27 (These always equals to 27, Sequence of them are 1,4,2,8,5,7 that can be obtain from *1 devide by 7*)
258+741=999 (Sum of Left 3-Digits and Right 3-Digits always equal to 999)
25+87+41=153 (It should be 99, The digits are out of sequence), So It can be corrected to prove the *Numbers are from Cyclic Numbers* by Overlap Addition and its Reverse Digits of each 2-Digits Integers,
Like: 153=15+53=68, so 68+86=154=15+54=69, so 69+96=165=16+65=81, so 81+18=99 (*Hence Proved)
So Answer to your query is 142857 and you double it you get 285,714. Every couple of numbers that has Cyclic Properties and consists of 1,2,4,5,7,8 could be good candidates.
You are dealing with a Cyclic Numbers in your given Example. Like you are mentioning 258,741 so, Here are some interesting properties of Cyclic Numbers:
2+5+8+7+4+1=27 (These always equals to 27, Sequence of them are 1,4,2,8,5,7 that can be obtain from *1 devide by 7*)
258+741=999 (Sum of Left 3-Digits and Right 3-Digits always equal to 999)
25+87+41=153 (It should be 99, The digits are out of sequence), So It can be corrected to prove the *Numbers are from Cyclic Numbers* by Overlap Addition and its Reverse Digits of each 2-Digits Integers,
Like: 153=15+53=68, so 68+86=154=15+54=69, so 69+96=165=16+65=81, so 81+18=99 (*Hence Proved)
So Answer to your query is 142857 and you double it you get 285,714. Every couple of numbers that has Cyclic Properties and consists of 1,2,4,5,7,8 could be good candidates.