110 110 110 110 110 110 110 110 1
101 101 101 101 101 101 101 101 1
The sum of N whole numbers being odd or even only depends on each of the numbers being odd or even. So we use 0 and 1, but:
- any 0 can be replaced with any even number
- any 1 can be replace with any odd number.
Since we need any 3 successive numbers to be even, we need a repeating pattern of 3 numbers.
:
The possible values of a 3 digit-pattern using only 0 and 1 are:
000
even
001
odd
010
odd
011
even
100
odd
101
even
110
even
111
odd
That leaves us with000
,011
,101
and110
:
000 000
-> the sum of any 3 consecutive digits (always000
) is even.
011 011
-> the 3 consecutive digits can be either011
,110
or101
, all 3 sums are even.
101 101
-> it's the same 3 groups just offset by 1
110 110
-> ditto
Another way of getting this list is considering that to get an even sum of 3 digits, we need either
any 0 can be replaced with any even number any 1 can be replace with any odd number. Only even digits (0 ->
Since we need any 3 successive numbers to be even, we need a repeating pattern of 3 numbers.
The possible values of a 3 digit-pattern using only 0 and 1 are:
000
even
001
odd
010
odd
011
even
100
odd
101
even
110
even
111
odd
That leaves us with000
,011
,101
and110
:
000 000
-> the sum of any 3 consecutive digits (always000
) is even.
011 011
-> the 3 consecutive digits can be either011
,110
or101
, all 3 sums are even.
101 101
-> it's the same 3 groups just offset by 1
110 110
-> ditto
Another way of getting this list is considering that to get an even sum of 3 digits, we need either:
000
)Two odd digits (1, the sum of which will be even) and one even digit (0) -> 011
,101
or110
.
Now, by repeating 8 times either of these 4 patterns, we get a series of 24 numbers where the sum of any 3 consecutive numbers is even. Clearly the sum of all 24 numbers is even as well.
We still need to add one digit, and for the sum of all numbers to be odd. This condition means the last digit must be 1.
Since we need to continue repeating our pattern, it means the pattern must start with 1, which only leaves us101
and110
.
Now, by repeating 8 times either of these 4 patterns, we get a series of 24 numbers where the sum of any 3 consecutive numbers is even. Clearly the sum of all 24 numbers is even as well.
We still need to add one digit, and for the sum of all numbers to be odd. This condition means the last digit must be 1.
Since we need to continue repeating our pattern, it means the pattern must start with 1, which only leaves us
101
and 110
.