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# Interesting numbers

Bikerman
Here's a very interesting number: 142,857

Multiply by 2, 3. 4, 5 and 6 and in each case the answer is a rearrangement of the same digits.
Multiply by 7 = 999,999
Multiply by 8 = 1,142,856 - take the 1 from the left and add it to the right (units) - back to the original digits.
Multiply by 9 = 1,285,713 - ditto
Multiply by 11,12,13 ditto
ankur2010
Hahaha...[]

Good one...
kitsrock
Speaking of weird numbers, a few weeks ago I came across this site. It's a list of other interesting numbers. While some aren't as interesting as they claim, I found 'right-truncatable prime' quite interesting.

 Quote: 73939133 is the largest prime for which all the initial segments of the decimal expansion are also prime (7, 73, 739, ...). So even if we stop writing before we finish the number, we have still written a prime! Such primes are called right-truncatable primes. (If we allow 1 to be considered a prime, then the largest are 1979339333 and 1979339339.)

source: http://primes.utm.edu/glossary/page.php?sort=RightTruncatablePrime

If you follow the source link, there's a link near the bottom to left-truncatable primes (same, but from left) like 4632647, and deletable prime (ordered deletion of digits where each is a prime)
ofertas
prime numbers is key for almost algorithms
Bikerman
Well, the BBC series on Radio4 is well worth a listen for all numberphiles.
http://bikerman.co.uk/index.php/science/audio/interesting-numbers
Cliffer
someboday dislike 13? really? and how about you?
ProwerBot
Think of a number
Double it
Divide by 2
Subtract first number

Strange how there's just weird formulas like this eh?
Cliffer
do you like 4?
bukaida
 ProwerBot wrote: Think of a number Double it Add 10 Divide by 2 Subtract first number answer is 5. Strange how there's just weird formulas like this eh?

It is a simple algebric equation. Think of a number say X. Multiply by 2 = 2X

Divide by 2= X+5

Subtract 5= X+5-5=X

You can construct 100s like this.

But the numbers in the first post are unique of it's kind.

However there are many interesting problems associated with numbers and their digits. Thats why mathematics is so beautiful and amazing.
socials
Really nice what math can do. There are some secrets that no everyone know. Thanks for sharing.
Bikerman
Some more interesting patterns with numbers:
11
11^2= 121
11^3= 12321
11^4= 1234321
11^5= 123454321
etc...

1*8 + 1 = 9
12*8 + 2 = 98
123*8 + 3 = 987
1234*8 + 4 = 9876
12345*8 + 5 = 98765
123456*8 + 6 = 987654
1234567*8 + 7 = 9876543
12345678*8 + 8 = 98765432
123456789*8 + 9 = 987654321

12345679*9 = 111111111
12345679*18 = 222222222
12345679*27 = 333333333
12345679*36 = 444444444
12345679*45 = 555555555
12345679*54 = 666666666
12345679*63 = 777777777
12345679*72 = 888888888
12345679*81 = 999999999
cybersa
 Bikerman wrote: Some more interesting patterns with numbers: 11 11^2= 121 11^3= 12321 11^4= 1234321 11^5= 123454321 etc... 1*8 + 1 = 9 12*8 + 2 = 98 123*8 + 3 = 987 1234*8 + 4 = 9876 12345*8 + 5 = 98765 123456*8 + 6 = 987654 1234567*8 + 7 = 9876543 12345678*8 + 8 = 98765432 123456789*8 + 9 = 987654321 12345679*9 = 111111111 12345679*18 = 222222222 12345679*27 = 333333333 12345679*36 = 444444444 12345679*45 = 555555555 12345679*54 = 666666666 12345679*63 = 777777777 12345679*72 = 888888888 12345679*81 = 999999999

Nice.
Where you got all these things?
saberlivre
 cybersa wrote: Nice. Where you got all these things?

I'm curious to know too ...............
kelseymh
 Bikerman wrote: Some more interesting patterns with numbers: 11 11^2= 121 11^3= 12321 11^4= 1234321 11^5= 123454321 etc...

Um, these are wrong. The powers of 11 trace out the binomial coefficients, or equivalently the vertices of Pascal's triangle:

11^2 = 121
11^3 = 1331
11^4 = 14641

after this, the nice digit pattern breaks down since 4+6 = 10.
Bikerman
LOL...that's me being a dumbass and typing one thing whilst reading another
It SHOULD go:
1*1 = 1
11*11 = 121
111*111 = 12321
1111*1111 = 1234321
11111*11111 = 123454321
111111*111111 = 12345654321
1111111*1111111 = 1234567654321
11111111*11111111 = 123456787654321
111111111*111111111 = 12345678987654321
asnani04
Great one man! seems like you are very interested in patterns!
therimalaya
Ha Ha Ha...
This is all interesting, Mathematics is a beautiful puzzle
Bikerman
If you want a source for great number problems and the like then I recommend:
Math Wonders to Inspire Teachers and Students by Alfred S. Posamentier