sábado, 16 de julio de 2016
jueves, 23 de junio de 2016
Tau Numbers
Tau numbers are those that number of divisors of n divides n
You can see the definition here A033950 and the list of the first 10,000 of these numbers here.
The current year, 2016, is one of these numbers because the number of divisors of 2016 is 36, and 2016/36 = 56.
If we subtract from 2016 his number of divisors 36, we obtain 1980, which is also a number Tau.
We follow with the same procedure with the numbers obtained while Tau numbers are obtain.
2016 (36) -> 1980 (36) ---> 1944 (24) ---> 1920 (32) and here the chain ends because 1888 is not a number Tau.
We can say that 2016 generates (counting himself) four numbers Tau.
What is the longest string of numbers Tau that applying this methodology can be found?
Spanish Version : 1453 - Números Tau
You can see the definition here A033950 and the list of the first 10,000 of these numbers here.
The current year, 2016, is one of these numbers because the number of divisors of 2016 is 36, and 2016/36 = 56.
If we subtract from 2016 his number of divisors 36, we obtain 1980, which is also a number Tau.
We follow with the same procedure with the numbers obtained while Tau numbers are obtain.
2016 (36) -> 1980 (36) ---> 1944 (24) ---> 1920 (32) and here the chain ends because 1888 is not a number Tau.
We can say that 2016 generates (counting himself) four numbers Tau.
What is the longest string of numbers Tau that applying this methodology can be found?
Spanish Version : 1453 - Números Tau
lunes, 13 de junio de 2016
Multiples with all the digits
Find for each prime, the sequence of multiples of this prime with the
least sum, which contains each of the digits from 0 to 9, one and only
one time.
Examples
For 2 : 14, 36, 58, 70, 92. Sum = 270
For 3 : 12, 39, 48, 57, 60. Sum = 216
For 5 : 12345, 67890 . Sum = 80235
For 7 : 63, 70, 189, 245 . Sum = 567
For 11: 165, 704, 2398 . Sum = 3267
Can you check if this secuences are that with the least sum ?
Can you find the sequences for larger primes?
Update: Mmonchi and Vicente found this values
For 3: 6, 9, 18, 27, 30, 45 (135)
For 5: 13685, 24790 (38475) Mmonchi
For 7: 7, 28, 49, 63, 105 (252) Mmonchi
For 11: 264,539,1078 (1881) Vicente
For 13: 26, 78, 195, 403 (702) Mmonchi
For 17: 34, 85, 102, 697 (918) Mmonchi
For 19: 19, 76, 285, 304 (684) Mmonchi
For 23: 46,92,713,805 (1656) Vicente
For 29: 493,580,1276 (2349) Vicente.
For 31: 372,496,1085 (1953) Vicente.
Spanish version : 1450 - Múltiplos con todos los dígitos
Examples
For 2 : 14, 36, 58, 70, 92. Sum = 270
For 3 : 12, 39, 48, 57, 60. Sum = 216
For 5 : 12345, 67890 . Sum = 80235
For 7 : 63, 70, 189, 245 . Sum = 567
For 11: 165, 704, 2398 . Sum = 3267
Can you check if this secuences are that with the least sum ?
Can you find the sequences for larger primes?
Update: Mmonchi and Vicente found this values
For 3: 6, 9, 18, 27, 30, 45 (135)
For 5: 13685, 24790 (38475) Mmonchi
For 7: 7, 28, 49, 63, 105 (252) Mmonchi
For 11: 264,539,1078 (1881) Vicente
For 13: 26, 78, 195, 403 (702) Mmonchi
For 17: 34, 85, 102, 697 (918) Mmonchi
For 19: 19, 76, 285, 304 (684) Mmonchi
For 23: 46,92,713,805 (1656) Vicente
For 29: 493,580,1276 (2349) Vicente.
For 31: 372,496,1085 (1953) Vicente.
Spanish version : 1450 - Múltiplos con todos los dígitos
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