A digit is a single number.
For example: 0 to 9 are single digits.
The sixth digit of the NAICS code is used to define national industries
25811 is a single (5-digit) number and a single number does not 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.
29513101917 is a single 11-digit number. A single number cannot define a sequence.
13227451532 is a single 11-digit number. A single number cannot define a sequence.
03815 is a single 5-digit number. A single number cannot define a sequence.
81 is a single 2-digit number. A single number cannot define a sequence.
01246 is a single 5-digit number. A single number cannot define a sequence.
312 is not a sequence: it is a single 3 digit integer and one number cannot define a sequence.
in ones digit arithmetic to define a+b you take the integer a+b and drop all but the one's digit (same for a x b). 1+2+3+4+5+6+7=8 because you drop all but the one's digit.