Sum of all positive integers having twice as many digits when written in base $2$ as they have when written is base $3$ is 10.
This is because the only two integers which fits the constraint are 2 and 8,
2 in base 10 =10 in base 2 = 2 in base 3
8 in base 10 =1000 in base 2 = 22 in base 3.
The result of the expression $a+b$ is 11
This is because the LCM of [1!+2!, 2!+3!, 3!+4!, 4!+5!, 5!+6!, 6!+7!, 7!+8!, 8!+9!] =3,628,800
Which can be written as : 1. 10! = 1 + 10 = 11
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