317.
Let's list the above number in ascending order by taking one digit, two digits, and three digits at a time, respectively.
One digit numbers: 1,3,7
Two digit numbers : 13,17,31,37,71,73
Three digit numbers: 137,173,317,371,713,731.
Now here comes the beauty. Numbers that are less than 317 (including 317) are prime (the number 1 is considered to be prime here in this context)! Numbers greater than 317 are composite! But what is so special about the number 317?
That's my hostel room number :P.
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Brilliant! ...too calculative! :)
ReplyDelete:D, it sums to a prime too ;)
ReplyDelete