This is a recursively defined sequence of numbers which is commonly called as Look and say sequence.
The sequence can be defined as:
# Take a decimal number # Look at the number, group consecutive runs of the same digit. # Say the number, from left to right, group by group; as how many of that digit there are - followed by the digit grouped. # This becomes the next number of the sequence.
3 = one three 13 = one one, one three 1113 = three one, one three 3113 = one three, two one, one three 132113 = one one, one three, one two, two one, one three 1113122113 = three one, one three, one one,two two, two one, one three 311311222113 = one three, two one, one three, two one, three two, two one, one three 13211321322113
So the next number in this look and say sequence is 13211321322113
13211321322113