Prime Numbers
(numbers that have exactly two factors, 1 and the number itself; 1 is no prime number because it has only one factor)
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 173 179 181 191 193 197 199 211 223 227 229 233 239 241 251 257 ...
There are an infinite number of prime numbers, but no formula for calculating one after another.