14
OKT
2008
OKT
2008
What would we do without referrers? I do not really know, but bloggers would have to do without a lot of funny search requests.
A few days ago, someon was looking for a Rechenregel wie man erkennt durch welche Zahlen eine Zahl teilbar ist. That roughly translates as rule how to recognize by which numbers a number is divisible. Anyway, I am happy to provide a few. All rules are equivalencies, that is the given number is divisible if the rule is fulfilled; otherwise, it is not divisible.
- every number is divisible by one 🙂
- the final digit is divisible by two
- the cross total (sum of digits) is divisible by three
- the number comprised of the final two digits is divisible by four
- the final digit is zero or five
- both rules 2 and 3 hold
- double the final digit and subtract it from the rest of the number; the result is divisible by seven; e.g. 203: 20-2*3=14 is divisible
- the number comprised of the final three digits is divisible by eight
- the cross total is divisible by nine
- the final digit is zero
- the alternating sum of digits is divisible by eleven, e.g. 135795: 1-3+5-7+9-5=0 is divisible
- rules 3 and 4 hold
- quadruple the final digit and add it to rest of the number; the result is divisible by thirteen; e.g. 403: 40+4*3=52; it is useful to apply the rule again: 5+4*2=13 isdivisible, so 52 is, and therefore 403 as well.
Well, that should suffice for now.
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