if repeating is allowed... 36 (6x6, for the last two digits) If not, 6 (3x2, last two digits)
312 is a single, 3-digit number. It is not a sequence.
3591733 is a 7-digit number. A single number cannot define a sequence.
The first four-digit Fibonacci number is 1597 - equal to 610 + 987.
10 digits to select for the first number in the sequence 10 digits to select for the second number in the sequence for each possible option of 10 digits in the first slot in the sequence (10 * 10) 10 digits to select for the third number in the sequence for each possible option of 10 digits in the second slot for each possible digit in the first slot of the sequence (or more easily put, 10 possible digits for each of 100 potential first two number sequences) [10*10*10] etc.... =10 * 10 * 10 * 10 * 10 * 10 * 10 = 10^7 = 10,000,000 (10 Million) Now add an area code before that 7 digit phone number and you get 10 Billion combinations (of course there are exclusions such as any sequence starting in 911 would be prohibited which is a reduction of 10 million numbers itself - 911 000 0001, 911 000 0002, etc. There are many other exclusions as well such as can't start with 0 - this removes another 1 billion sequences)
if repeating is allowed... 36 (6x6, for the last two digits) If not, 6 (3x2, last two digits)
It is not a sequence but a single 7-digit number.
25811 is a single (5-digit) number and a single number does not define a sequence.
312 is a single, 3-digit number. It is not a sequence.
691215 is not a sequence: it is a single 6-digit number.
13227451532 is a single 11-digit number. A single number cannot define a sequence.
29513101917 is a single 11-digit number. A single number cannot define a sequence.
12436871416 is a single 11-digit number. A single number does not define a sequence.
3591733 is a 7-digit number. A single number cannot define a sequence.
133514221125715124 is a single 18-digit number. A single number cannot define a sequence.
03815 is a single 5-digit number. A single number cannot define a sequence.
5111729 is a single 7-digit number. A single number does not make a sequence.