How fast does it terminate?

Logic Level 2

178 , 56 , 30 , ? \huge \color{#3D99F6} {178},\color{#D61F06} {56},\color{#20A900} {30},?

What is the next number in this sequence?


The answer is 0.

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15 solutions

1 x 7 x 8 = 56

5 x 6 = 30

3 x 0 = 0

Moderator note:

Simple and elegant. Can the same rule apply for all preceding terms? That is, does there exist a number before the number 178 178 ? Why or why not?

No preceding terms. 178 can be factored only as 2 * 89.

Narayanan CT - 5 years, 10 months ago

178 = 2 89 178=2*89 , 89 89 isn't a 1-digit number, therefore the number before 178 178 doesn't exist.

Trí Onii-sama - 6 years, 1 month ago

What the .....

Mohamed Asem - 5 years, 10 months ago

The same rule cannot be applied for preceeding terms because 178 is the product of the primes 89 and 2, and since the process involves multiplying each digit of a number, 892 would preceed 8 9 2=144

Jon Bushman - 5 years, 10 months ago

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the product of 2 and 89 is 178 not 177.

Rizwan Shah - 5 years, 10 months ago

@Challenge Master, Since The Prime Factorization of 178 is 2 × 89 2 \times 89 and 89 is not a 1 digit number, Hence, A number before 178 Doesn't exist. ¨ \ddot\smile

Mehul Arora - 6 years, 1 month ago

I believe that for this kind of problem, the simplest solution is the best. However, I would like to propose an alternative solution that satisfies this pattern, including the 'no term could come before 178' condition.

Here is the solution:

Let n denote index of each term. For n = 1: a n = 178 a_{n}=178

For n > 1:

a n = 134 n + 154 n 1 a n 1 134 n + 154 n 1 a n 1 × a n 1 ( n 1 ) 22 ( 7 2 n ) n \boxed{a_{n}=\frac{\frac{134n+154}{n-1}-a_{n-1}}{\frac{134n+154}{n-1}-a_{n-1}} \times \frac{a_{n-1}(n-1)-22(7-2n)}{n}}

For instance:

a 2 = 134 ( 2 ) + 154 2 1 178 134 ( 2 ) + 154 2 1 178 × 178 ( 2 1 ) 22 ( 7 2 ( 2 ) ) 2 = 56 a_{2}=\frac{\frac{134(2)+154}{2-1}-178}{\frac{134(2)+154}{2-1}-178} \times \frac{178(2-1)-22(7-2(2))}{2}=56

a 3 = 134 ( 3 ) + 154 3 1 56 134 ( 3 ) + 154 3 1 56 × 56 ( 3 1 ) 22 ( 7 2 ( 3 ) ) 3 = 30 a_{3}=\frac{\frac{134(3)+154}{3-1}-56}{\frac{134(3)+154}{3-1}-56} \times \frac{56(3-1)-22(7-2(3))}{3}=30

Therefore,

a 4 = 134 ( 4 ) + 154 4 1 30 134 ( 4 ) + 154 4 1 30 × 30 ( 4 1 ) 22 ( 7 2 ( 4 ) ) 4 = 28 a_{4}=\frac{\frac{134(4)+154}{4-1}-30}{\frac{134(4)+154}{4-1}-30} \times \frac{30(4-1)-22(7-2(4))}{4}=28

To sum up, except for 0, the other possible answer is 28 .

Zain Lohani
May 5, 2015

Multiply every digit in a number to get next number in sequence.

Saddam Hossain
Dec 5, 2015

1x7x8=56,5x6=30 & 3x0=0. So, answer is 0.

see... 1 7 8=56, 5 6=30 and now 3 0= 0... so 0 is the answer

Sarika Singh
Jul 29, 2015

1 * 7 * 8=56

5*6=30

3*0=0

Rizwan Shah
Jul 28, 2015

1 x 7 x 8 = 56 then 5 x 6 = 30 next 3 x 0 = 0 so next number is 0.

Hadia Qadir
Jul 28, 2015

1 x 7 x 8 = 56 5 x 6 = 30 3 x 0 = 0 so easy

Vraj Mistry
Jun 12, 2015

178,56,30,0

1st Term=178

2nd Term=1x7x8=56

3rd Term=5x6=30

4th Term=3x0=0

Clavin Rali
May 15, 2015

The heading says it all !!!!

Please change the title !

Arafe Sajid
May 13, 2015

1 7 8=56 5 6=30 3 0=0

just multiply each number so that you can get the next number. Like 1st number is

178 so

1 *7 *8 =56 = 2nd number

56= 5*6= 30 3rd number

30=3*0= 0 next number

Sotonwa Olawale
May 5, 2015

1 *7 *8 =56

5 * 6=30

3 * 0=0

Gamal Sultan
May 5, 2015

The product of the digits of any number gives the next one

Just have to multiply last two digits of each number

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